[PATCH] f2fs: fix to do sanity check on last xattr entry in __f2fs_setxattr()

[PATCH] f2fs: fix to do sanity check on last xattr entry in __f2fs_setxattr()

[Chao Yu]

As Wenqing Liu reported in bugzilla:

https://bugzilla.kernel.org/show_bug.cgi?id=215235

- Overview
page fault in f2fs_setxattr() when mount and operate on corrupted image

- Reproduce
tested on kernel 5.16-rc3, 5.15.X under root

1. unzip tmp7.zip
2. ./single.sh f2fs 7

Sometimes need to run the script several times

- Kernel dump
loop0: detected capacity change from 0 to 131072
F2FS-fs (loop0): Found nat_bits in checkpoint
F2FS-fs (loop0): Mounted with checkpoint version = 7548c2ee
BUG: unable to handle page fault for address: ffffe47bc7123f48
RIP: 0010:kfree+0x66/0x320
Call Trace:
 __f2fs_setxattr+0x2aa/0xc00 [f2fs]
 f2fs_setxattr+0xfa/0x480 [f2fs]
 __f2fs_set_acl+0x19b/0x330 [f2fs]
 __vfs_removexattr+0x52/0x70
 __vfs_removexattr_locked+0xb1/0x140
 vfs_removexattr+0x56/0x100
 removexattr+0x57/0x80
 path_removexattr+0xa3/0xc0
 __x64_sys_removexattr+0x17/0x20
 do_syscall_64+0x37/0xb0
 entry_SYSCALL_64_after_hwframe+0x44/0xae

The root cause is in __f2fs_setxattr(), we missed to do sanity check on
last xattr entry, result in out-of-bound memory access during updating
inconsistent xattr data of target inode.

After the fix, it can detect such xattr inconsistency as below:

F2FS-fs (loop11): inode (7) has invalid last xattr entry, entry_size: 60676
F2FS-fs (loop11): inode (8) has corrupted xattr
F2FS-fs (loop11): inode (8) has corrupted xattr
F2FS-fs (loop11): inode (8) has invalid last xattr entry, entry_size: 47736

Cc: stable@vger.kernel.org
Reported-by: Wenqing Liu <wenqingliu0120@gmail.com>
Signed-off-by: Chao Yu <chao@kernel.org>
---
 fs/f2fs/xattr.c | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/fs/f2fs/xattr.c b/fs/f2fs/xattr.c
index e348f33bcb2b..c544100643c8 100644
--- a/fs/f2fs/xattr.c
+++ b/fs/f2fs/xattr.c
@@ -684,8 +684,17 @@ static int __f2fs_setxattr(struct inode *inode, int index,
 	}
 
 	last = here;
-	while (!IS_XATTR_LAST_ENTRY(last))
+	while (!IS_XATTR_LAST_ENTRY(last)) {
+		if ((void *)(last) + sizeof(__u32) > last_base_addr ||
+			(void *)XATTR_NEXT_ENTRY(last) > last_base_addr) {
+			f2fs_err(F2FS_I_SB(inode), "inode (%lu) has invalid last xattr entry, entry_size: %lu",
+					inode->i_ino, ENTRY_SIZE(last));
+			set_sbi_flag(F2FS_I_SB(inode), SBI_NEED_FSCK);
+			error = -EFSCORRUPTED;
+			goto exit;
+		}
 		last = XATTR_NEXT_ENTRY(last);
+	}
 
 	newsize = XATTR_ALIGN(sizeof(struct f2fs_xattr_entry) + len + size);
 
-- 
2.32.0