[Bug 1877688] [NEW] 9p virtfs device reports error when opening certain files

[Bug 1877688] [NEW] 9p virtfs device reports error when opening certain files

[A A]

Public bug reported:

Reading certain files on a 9p mounted FS produces this error message:

qemu-system-x86_64: VirtFS reply type 117 needs 12 bytes, buffer has 12,
less than minimum

After this error message is generated, further accesses to the 9p FS
hangs whatever tries to access it. The Arch Linux guest system is
otherwise usable. This happens with QEMU 5.0.0 and guest kernel version
5.6.11, hosted on an Arch Linux distro. I use the following command to
launch QEMU:

exec qemu-system-x86_64 -enable-kvm -display gtk -vga virtio -cpu host
-m 4G -netdev tap,ifname=vmtap0,id=vn0,script=no,downscript=no -device
virtio-net-pci,netdev=vn0 -kernel kernel.img -drive
file=file.img,format=raw,if=virtio -virtfs
local,path=mnt,mount_tag=host0,security_model=passthrough,id=host0
-append "console=ttyS0 root=/dev/vda rw"

There's nothing relevant in the guest kernel logs as far as I'm aware of
with loglevel set to 7.

** Affects: qemu
     Importance: Undecided
         Status: New


** Tags: 9p virtfs

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Title:
  9p virtfs device reports error when opening certain files

Status in QEMU:
  New

Bug description:
  Reading certain files on a 9p mounted FS produces this error message:

  qemu-system-x86_64: VirtFS reply type 117 needs 12 bytes, buffer has
  12, less than minimum

  After this error message is generated, further accesses to the 9p FS
  hangs whatever tries to access it. The Arch Linux guest system is
  otherwise usable. This happens with QEMU 5.0.0 and guest kernel
  version 5.6.11, hosted on an Arch Linux distro. I use the following
  command to launch QEMU:

  exec qemu-system-x86_64 -enable-kvm -display gtk -vga virtio -cpu host
  -m 4G -netdev tap,ifname=vmtap0,id=vn0,script=no,downscript=no -device
  virtio-net-pci,netdev=vn0 -kernel kernel.img -drive
  file=file.img,format=raw,if=virtio -virtfs
  local,path=mnt,mount_tag=host0,security_model=passthrough,id=host0
  -append "console=ttyS0 root=/dev/vda rw"

  There's nothing relevant in the guest kernel logs as far as I'm aware
  of with loglevel set to 7.

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[Bug 1877688] Re: 9p virtfs device reports error when opening certain files

[A A]

** Description changed:

  Reading certain files on a 9p mounted FS produces this error message:
  
  qemu-system-x86_64: VirtFS reply type 117 needs 12 bytes, buffer has 12,
  less than minimum
  
  After this error message is generated, further accesses to the 9p FS
  hangs whatever tries to access it. The Arch Linux guest system is
  otherwise usable. This happens with QEMU 5.0.0 and guest kernel version
  5.6.11, hosted on an Arch Linux distro. I use the following command to
  launch QEMU:
  
  exec qemu-system-x86_64 -enable-kvm -display gtk -vga virtio -cpu host
  -m 4G -netdev tap,ifname=vmtap0,id=vn0,script=no,downscript=no -device
  virtio-net-pci,netdev=vn0 -kernel kernel.img -drive
  file=file.img,format=raw,if=virtio -virtfs
  local,path=mnt,mount_tag=host0,security_model=passthrough,id=host0
  -append "console=ttyS0 root=/dev/vda rw"
  
  There's nothing relevant in the guest kernel logs as far as I'm aware of
  with loglevel set to 7.
+ 
+ Aha, I found the cursed file. See this strace log:
+ 
+ openat(AT_FDCWD, "/home/user/.local/share/nvim/shada/main.shada", O_RDONLY|O_CLOEXEC) = 25
+ mmap(NULL, 880640, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f3ab8427000
+ mmap(NULL, 880640, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f3ab8350000
+ mmap(NULL, 880640, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f3ab8279000
+ mmap(NULL, 880640, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f3ab81a2000
+ mmap(NULL, 880640, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f3ab80cb000
+ readv(25,

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Title:
  9p virtfs device reports error when opening certain files

Status in QEMU:
  New

Bug description:
  Reading certain files on a 9p mounted FS produces this error message:

  qemu-system-x86_64: VirtFS reply type 117 needs 12 bytes, buffer has
  12, less than minimum

  After this error message is generated, further accesses to the 9p FS
  hangs whatever tries to access it. The Arch Linux guest system is
  otherwise usable. This happens with QEMU 5.0.0 and guest kernel
  version 5.6.11, hosted on an Arch Linux distro. I use the following
  command to launch QEMU:

  exec qemu-system-x86_64 -enable-kvm -display gtk -vga virtio -cpu host
  -m 4G -netdev tap,ifname=vmtap0,id=vn0,script=no,downscript=no -device
  virtio-net-pci,netdev=vn0 -kernel kernel.img -drive
  file=file.img,format=raw,if=virtio -virtfs
  local,path=mnt,mount_tag=host0,security_model=passthrough,id=host0
  -append "console=ttyS0 root=/dev/vda rw"

  There's nothing relevant in the guest kernel logs as far as I'm aware
  of with loglevel set to 7.

  Aha, I found the cursed file. See this strace log:

  openat(AT_FDCWD, "/home/user/.local/share/nvim/shada/main.shada", O_RDONLY|O_CLOEXEC) = 25
  mmap(NULL, 880640, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f3ab8427000
  mmap(NULL, 880640, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f3ab8350000
  mmap(NULL, 880640, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f3ab8279000
  mmap(NULL, 880640, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f3ab81a2000
  mmap(NULL, 880640, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f3ab80cb000
  readv(25,

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[Bug 1877688] Re: 9p virtfs device reports error when opening certain files

[A A]

Here's a C program to trigger this behavior. I don't think it matters
what the contents of "file" or its size is.

** Description changed:

  Reading certain files on a 9p mounted FS produces this error message:
  
  qemu-system-x86_64: VirtFS reply type 117 needs 12 bytes, buffer has 12,
  less than minimum
  
  After this error message is generated, further accesses to the 9p FS
  hangs whatever tries to access it. The Arch Linux guest system is
  otherwise usable. This happens with QEMU 5.0.0 and guest kernel version
  5.6.11, hosted on an Arch Linux distro. I use the following command to
  launch QEMU:
  
  exec qemu-system-x86_64 -enable-kvm -display gtk -vga virtio -cpu host
  -m 4G -netdev tap,ifname=vmtap0,id=vn0,script=no,downscript=no -device
  virtio-net-pci,netdev=vn0 -kernel kernel.img -drive
  file=file.img,format=raw,if=virtio -virtfs
  local,path=mnt,mount_tag=host0,security_model=passthrough,id=host0
  -append "console=ttyS0 root=/dev/vda rw"
  
  There's nothing relevant in the guest kernel logs as far as I'm aware of
  with loglevel set to 7.
  
- Aha, I found the cursed file. See this strace log:
- 
- openat(AT_FDCWD, "/home/user/.local/share/nvim/shada/main.shada", O_RDONLY|O_CLOEXEC) = 25
- mmap(NULL, 880640, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f3ab8427000
- mmap(NULL, 880640, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f3ab8350000
- mmap(NULL, 880640, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f3ab8279000
- mmap(NULL, 880640, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f3ab81a2000
- mmap(NULL, 880640, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f3ab80cb000
- readv(25,
+ I tracked down the issue to readv() with a small buffer(<=12 bytes) and
+ then a large buffer(>= 1024 bytes). A C program is provided to trigger
+ this behavior.

** Attachment added: "readv.c"
   https://bugs.launchpad.net/qemu/+bug/1877688/+attachment/5368749/+files/readv.c

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Title:
  9p virtfs device reports error when opening certain files

Status in QEMU:
  New

Bug description:
  Reading certain files on a 9p mounted FS produces this error message:

  qemu-system-x86_64: VirtFS reply type 117 needs 12 bytes, buffer has
  12, less than minimum

  After this error message is generated, further accesses to the 9p FS
  hangs whatever tries to access it. The Arch Linux guest system is
  otherwise usable. This happens with QEMU 5.0.0 and guest kernel
  version 5.6.11, hosted on an Arch Linux distro. I use the following
  command to launch QEMU:

  exec qemu-system-x86_64 -enable-kvm -display gtk -vga virtio -cpu host
  -m 4G -netdev tap,ifname=vmtap0,id=vn0,script=no,downscript=no -device
  virtio-net-pci,netdev=vn0 -kernel kernel.img -drive
  file=file.img,format=raw,if=virtio -virtfs
  local,path=mnt,mount_tag=host0,security_model=passthrough,id=host0
  -append "console=ttyS0 root=/dev/vda rw"

  There's nothing relevant in the guest kernel logs as far as I'm aware
  of with loglevel set to 7.

  I tracked down the issue to readv() with a small buffer(<=12 bytes)
  and then a large buffer(>= 1024 bytes). A C program is provided to
  trigger this behavior.

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[Bug 1877688] Re: 9p virtfs device reports error when opening certain files

[Christian Schoenebeck]

Looks like being introduced by this change:
https://patchwork.kernel.org/patch/11319993/

More specifically this one exactly:

-    if (buf_size  < size) {
+    if (buf_size  < P9_IOHDRSZ) {

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Title:
  9p virtfs device reports error when opening certain files

Status in QEMU:
  New

Bug description:
  Reading certain files on a 9p mounted FS produces this error message:

  qemu-system-x86_64: VirtFS reply type 117 needs 12 bytes, buffer has
  12, less than minimum

  After this error message is generated, further accesses to the 9p FS
  hangs whatever tries to access it. The Arch Linux guest system is
  otherwise usable. This happens with QEMU 5.0.0 and guest kernel
  version 5.6.11, hosted on an Arch Linux distro. I use the following
  command to launch QEMU:

  exec qemu-system-x86_64 -enable-kvm -display gtk -vga virtio -cpu host
  -m 4G -netdev tap,ifname=vmtap0,id=vn0,script=no,downscript=no -device
  virtio-net-pci,netdev=vn0 -kernel kernel.img -drive
  file=file.img,format=raw,if=virtio -virtfs
  local,path=mnt,mount_tag=host0,security_model=passthrough,id=host0
  -append "console=ttyS0 root=/dev/vda rw"

  There's nothing relevant in the guest kernel logs as far as I'm aware
  of with loglevel set to 7.

  I tracked down the issue to readv() with a small buffer(<=12 bytes)
  and then a large buffer(>= 1024 bytes). A C program is provided to
  trigger this behavior.

To manage notifications about this bug go to:
https://bugs.launchpad.net/qemu/+bug/1877688/+subscriptions

[Bug 1877688] Re: 9p virtfs device reports error when opening certain files

[Christian Schoenebeck]

The following patch should fix this bug for the kvm backend (not for the
XEN backend yet).

Please let me know if it fixes this bug for you.

** Patch added: "bug1877688_kvm_fix.patch"
   https://bugs.launchpad.net/qemu/+bug/1877688/+attachment/5369130/+files/bug1877688_kvm_fix.patch

** Changed in: qemu
       Status: New => In Progress

** Changed in: qemu
     Assignee: (unassigned) => Christian Schoenebeck (schoenebeck)

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Title:
  9p virtfs device reports error when opening certain files

Status in QEMU:
  In Progress

Bug description:
  Reading certain files on a 9p mounted FS produces this error message:

  qemu-system-x86_64: VirtFS reply type 117 needs 12 bytes, buffer has
  12, less than minimum

  After this error message is generated, further accesses to the 9p FS
  hangs whatever tries to access it. The Arch Linux guest system is
  otherwise usable. This happens with QEMU 5.0.0 and guest kernel
  version 5.6.11, hosted on an Arch Linux distro. I use the following
  command to launch QEMU:

  exec qemu-system-x86_64 -enable-kvm -display gtk -vga virtio -cpu host
  -m 4G -netdev tap,ifname=vmtap0,id=vn0,script=no,downscript=no -device
  virtio-net-pci,netdev=vn0 -kernel kernel.img -drive
  file=file.img,format=raw,if=virtio -virtfs
  local,path=mnt,mount_tag=host0,security_model=passthrough,id=host0
  -append "console=ttyS0 root=/dev/vda rw"

  There's nothing relevant in the guest kernel logs as far as I'm aware
  of with loglevel set to 7.

  I tracked down the issue to readv() with a small buffer(<=12 bytes)
  and then a large buffer(>= 1024 bytes). A C program is provided to
  trigger this behavior.

To manage notifications about this bug go to:
https://bugs.launchpad.net/qemu/+bug/1877688/+subscriptions

[Bug 1877688] Re: 9p virtfs device reports error when opening certain files

[A A]

Thanks, it works.

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Title:
  9p virtfs device reports error when opening certain files

Status in QEMU:
  In Progress

Bug description:
  Reading certain files on a 9p mounted FS produces this error message:

  qemu-system-x86_64: VirtFS reply type 117 needs 12 bytes, buffer has
  12, less than minimum

  After this error message is generated, further accesses to the 9p FS
  hangs whatever tries to access it. The Arch Linux guest system is
  otherwise usable. This happens with QEMU 5.0.0 and guest kernel
  version 5.6.11, hosted on an Arch Linux distro. I use the following
  command to launch QEMU:

  exec qemu-system-x86_64 -enable-kvm -display gtk -vga virtio -cpu host
  -m 4G -netdev tap,ifname=vmtap0,id=vn0,script=no,downscript=no -device
  virtio-net-pci,netdev=vn0 -kernel kernel.img -drive
  file=file.img,format=raw,if=virtio -virtfs
  local,path=mnt,mount_tag=host0,security_model=passthrough,id=host0
  -append "console=ttyS0 root=/dev/vda rw"

  There's nothing relevant in the guest kernel logs as far as I'm aware
  of with loglevel set to 7.

  I tracked down the issue to readv() with a small buffer(<=12 bytes)
  and then a large buffer(>= 1024 bytes). A C program is provided to
  trigger this behavior.

To manage notifications about this bug go to:
https://bugs.launchpad.net/qemu/+bug/1877688/+subscriptions

[Bug 1877688] Re: 9p virtfs device reports error when opening certain files

[Christian Schoenebeck]

Fix is now committed on master as SHA-1 cf45183b718f02b1369e18c795dc51bc1821245d, which actually just reverted the mentioned commit that was leading to this broken behavior:
https://github.com/qemu/qemu/commit/cf45183b718f02b1369e18c795dc51bc1821245d

The original Xen transport bug that motivated that change, was now fixed differently by handling that Xen issue solely on Xen transport driver side:
https://github.com/qemu/qemu/commit/a4c4d462729466c4756bac8a0a8d77eb63b21ef7


** Changed in: qemu
       Status: In Progress => Fix Committed

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Title:
  9p virtfs device reports error when opening certain files

Status in QEMU:
  Fix Committed

Bug description:
  Reading certain files on a 9p mounted FS produces this error message:

  qemu-system-x86_64: VirtFS reply type 117 needs 12 bytes, buffer has
  12, less than minimum

  After this error message is generated, further accesses to the 9p FS
  hangs whatever tries to access it. The Arch Linux guest system is
  otherwise usable. This happens with QEMU 5.0.0 and guest kernel
  version 5.6.11, hosted on an Arch Linux distro. I use the following
  command to launch QEMU:

  exec qemu-system-x86_64 -enable-kvm -display gtk -vga virtio -cpu host
  -m 4G -netdev tap,ifname=vmtap0,id=vn0,script=no,downscript=no -device
  virtio-net-pci,netdev=vn0 -kernel kernel.img -drive
  file=file.img,format=raw,if=virtio -virtfs
  local,path=mnt,mount_tag=host0,security_model=passthrough,id=host0
  -append "console=ttyS0 root=/dev/vda rw"

  There's nothing relevant in the guest kernel logs as far as I'm aware
  of with loglevel set to 7.

  I tracked down the issue to readv() with a small buffer(<=12 bytes)
  and then a large buffer(>= 1024 bytes). A C program is provided to
  trigger this behavior.

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[Bug 1877688] Re: 9p virtfs device reports error when opening certain files

[Christian Schoenebeck]

Fixed in QEMU 5.1 release.

** Changed in: qemu
       Status: Fix Committed => Fix Released

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Title:
  9p virtfs device reports error when opening certain files

Status in QEMU:
  Fix Released

Bug description:
  Reading certain files on a 9p mounted FS produces this error message:

  qemu-system-x86_64: VirtFS reply type 117 needs 12 bytes, buffer has
  12, less than minimum

  After this error message is generated, further accesses to the 9p FS
  hangs whatever tries to access it. The Arch Linux guest system is
  otherwise usable. This happens with QEMU 5.0.0 and guest kernel
  version 5.6.11, hosted on an Arch Linux distro. I use the following
  command to launch QEMU:

  exec qemu-system-x86_64 -enable-kvm -display gtk -vga virtio -cpu host
  -m 4G -netdev tap,ifname=vmtap0,id=vn0,script=no,downscript=no -device
  virtio-net-pci,netdev=vn0 -kernel kernel.img -drive
  file=file.img,format=raw,if=virtio -virtfs
  local,path=mnt,mount_tag=host0,security_model=passthrough,id=host0
  -append "console=ttyS0 root=/dev/vda rw"

  There's nothing relevant in the guest kernel logs as far as I'm aware
  of with loglevel set to 7.

  I tracked down the issue to readv() with a small buffer(<=12 bytes)
  and then a large buffer(>= 1024 bytes). A C program is provided to
  trigger this behavior.

To manage notifications about this bug go to:
https://bugs.launchpad.net/qemu/+bug/1877688/+subscriptions