* [PATCH v3 0/2] vfs: better dedupe permission check @ 2018-06-07 17:38 Mark Fasheh 2018-06-07 17:38 ` [PATCH v3 1/2] vfs: allow dedupe of user owned read-only files Mark Fasheh 2018-06-07 17:38 ` [PATCH v3 2/2] vfs: dedupe should return EPERM if permission is not granted Mark Fasheh 0 siblings, 2 replies; 5+ messages in thread From: Mark Fasheh @ 2018-06-07 17:38 UTC (permalink / raw) To: Al Viro Cc: linux-fsdevel, linux-btrfs, linux-xfs, Darrick J . Wong, Adam Borowski, David Sterba Hi Al, The following patches fix a couple of issues with the permission check we do in vfs_dedupe_file_range(). I sent them out for review twice, a changelog is attached. If they look ok to you, I'd appreciate them being pushed upstream. You can get them from git if you like: git pull https://github.com/markfasheh/linux dedupe-perms The first patch expands our check to allow dedupe of a file if the user owns it or otherwise would be allowed to write to it. Current behavior is that we'll allow dedupe only if: - the user is an admin (root) - the user has the file open for write This makes it impossible for a user to dedupe their own file set unless they do it as root, or ensure that all files have write permission. There's a couple of duperemove bugs open for this: https://github.com/markfasheh/duperemove/issues/129 https://github.com/markfasheh/duperemove/issues/86 The other problem we have is also related to forcing the user to open target files for write - A process trying to exec a file currently being deduped gets ETXTBUSY. The answer (as above) is to allow them to open the targets ro - root can already do this. There was a patch from Adam Borowski to fix this back in 2016: https://lkml.org/lkml/2016/7/17/130 which I have incorporated into my changes. The 2nd patch fixes our return code for permission denied to be EPERM. For some reason we're returning EINVAL - I think that's probably my fault. At any rate, we need to be returning something descriptive of the actual problem, otherwise callers see EINVAL and can't really make a valid determination of what's gone wrong. This has also popped up in duperemove, mostly in the form of cryptic error messages. Because this is a code returned to userspace, I did check the other users of extent-same that I could find. Both 'bees' and 'rust-btrfs' do the same as duperemove and simply report the error (as they should). Please apply. Thanks, --Mark Changes from V2 to V3: - Return bool from allow_file_dedupe - V2 discussion: https://www.spinics.net/lists/linux-btrfs/msg78421.html Changes from V1 to V2: - Add inode_permission check as suggested by Adam Borowski - V1 discussion: https://marc.info/?l=linux-xfs&m=152606684017965&w=2 ^ permalink raw reply [flat|nested] 5+ messages in thread
* [PATCH v3 1/2] vfs: allow dedupe of user owned read-only files 2018-06-07 17:38 [PATCH v3 0/2] vfs: better dedupe permission check Mark Fasheh @ 2018-06-07 17:38 ` Mark Fasheh 2018-06-07 18:17 ` Darrick J. Wong 2018-06-07 17:38 ` [PATCH v3 2/2] vfs: dedupe should return EPERM if permission is not granted Mark Fasheh 1 sibling, 1 reply; 5+ messages in thread From: Mark Fasheh @ 2018-06-07 17:38 UTC (permalink / raw) To: Al Viro Cc: linux-fsdevel, linux-btrfs, linux-xfs, Darrick J . Wong, Adam Borowski, David Sterba, Mark Fasheh The permission check in vfs_dedupe_file_range() is too coarse - We only allow dedupe of the destination file if the user is root, or they have the file open for write. This effectively limits a non-root user from deduping their own read-only files. In addition, the write file descriptor that the user is forced to hold open can prevent execution of files. As file data during a dedupe does not change, the behavior is unexpected and this has caused a number of issue reports. For an example, see: https://github.com/markfasheh/duperemove/issues/129 So change the check so we allow dedupe on the target if: - the root or admin is asking for it - the process has write access - the owner of the file is asking for the dedupe - the process could get write access That way users can open read-only and still get dedupe. Signed-off-by: Mark Fasheh <mfasheh@suse.de> --- fs/read_write.c | 17 +++++++++++++++-- 1 file changed, 15 insertions(+), 2 deletions(-) diff --git a/fs/read_write.c b/fs/read_write.c index e83bd9744b5d..71e9077f8bc1 100644 --- a/fs/read_write.c +++ b/fs/read_write.c @@ -1964,6 +1964,20 @@ int vfs_dedupe_file_range_compare(struct inode *src, loff_t srcoff, } EXPORT_SYMBOL(vfs_dedupe_file_range_compare); +/* Check whether we are allowed to dedupe the destination file */ +static bool allow_file_dedupe(struct file *file) +{ + if (capable(CAP_SYS_ADMIN)) + return true; + if (file->f_mode & FMODE_WRITE) + return true; + if (uid_eq(current_fsuid(), file_inode(file)->i_uid)) + return true; + if (!inode_permission(file_inode(file), MAY_WRITE)) + return true; + return false; +} + int vfs_dedupe_file_range(struct file *file, struct file_dedupe_range *same) { struct file_dedupe_range_info *info; @@ -1972,7 +1986,6 @@ int vfs_dedupe_file_range(struct file *file, struct file_dedupe_range *same) u64 len; int i; int ret; - bool is_admin = capable(CAP_SYS_ADMIN); u16 count = same->dest_count; struct file *dst_file; loff_t dst_off; @@ -2036,7 +2049,7 @@ int vfs_dedupe_file_range(struct file *file, struct file_dedupe_range *same) if (info->reserved) { info->status = -EINVAL; - } else if (!(is_admin || (dst_file->f_mode & FMODE_WRITE))) { + } else if (!allow_file_dedupe(dst_file)) { info->status = -EINVAL; } else if (file->f_path.mnt != dst_file->f_path.mnt) { info->status = -EXDEV; -- 2.15.1 ^ permalink raw reply related [flat|nested] 5+ messages in thread
* Re: [PATCH v3 1/2] vfs: allow dedupe of user owned read-only files 2018-06-07 17:38 ` [PATCH v3 1/2] vfs: allow dedupe of user owned read-only files Mark Fasheh @ 2018-06-07 18:17 ` Darrick J. Wong 2018-06-07 20:45 ` Mark Fasheh 0 siblings, 1 reply; 5+ messages in thread From: Darrick J. Wong @ 2018-06-07 18:17 UTC (permalink / raw) To: Mark Fasheh Cc: Al Viro, linux-fsdevel, linux-btrfs, linux-xfs, Adam Borowski, David Sterba On Thu, Jun 07, 2018 at 10:38:53AM -0700, Mark Fasheh wrote: > The permission check in vfs_dedupe_file_range() is too coarse - We > only allow dedupe of the destination file if the user is root, or > they have the file open for write. > > This effectively limits a non-root user from deduping their own read-only > files. In addition, the write file descriptor that the user is forced to > hold open can prevent execution of files. As file data during a dedupe > does not change, the behavior is unexpected and this has caused a number of > issue reports. For an example, see: > > https://github.com/markfasheh/duperemove/issues/129 > > So change the check so we allow dedupe on the target if: > > - the root or admin is asking for it > - the process has write access > - the owner of the file is asking for the dedupe > - the process could get write access > > That way users can open read-only and still get dedupe. > > Signed-off-by: Mark Fasheh <mfasheh@suse.de> Looks ok, but could you please update the manpage for ioctl_fideduperange to elaborate on when userspace can expect EPERM? Acked-by: Darrick J. Wong <darrick.wong@oracle.com> --D > --- > fs/read_write.c | 17 +++++++++++++++-- > 1 file changed, 15 insertions(+), 2 deletions(-) > > diff --git a/fs/read_write.c b/fs/read_write.c > index e83bd9744b5d..71e9077f8bc1 100644 > --- a/fs/read_write.c > +++ b/fs/read_write.c > @@ -1964,6 +1964,20 @@ int vfs_dedupe_file_range_compare(struct inode *src, loff_t srcoff, > } > EXPORT_SYMBOL(vfs_dedupe_file_range_compare); > > +/* Check whether we are allowed to dedupe the destination file */ > +static bool allow_file_dedupe(struct file *file) > +{ > + if (capable(CAP_SYS_ADMIN)) > + return true; > + if (file->f_mode & FMODE_WRITE) > + return true; > + if (uid_eq(current_fsuid(), file_inode(file)->i_uid)) > + return true; > + if (!inode_permission(file_inode(file), MAY_WRITE)) > + return true; > + return false; > +} > + > int vfs_dedupe_file_range(struct file *file, struct file_dedupe_range *same) > { > struct file_dedupe_range_info *info; > @@ -1972,7 +1986,6 @@ int vfs_dedupe_file_range(struct file *file, struct file_dedupe_range *same) > u64 len; > int i; > int ret; > - bool is_admin = capable(CAP_SYS_ADMIN); > u16 count = same->dest_count; > struct file *dst_file; > loff_t dst_off; > @@ -2036,7 +2049,7 @@ int vfs_dedupe_file_range(struct file *file, struct file_dedupe_range *same) > > if (info->reserved) { > info->status = -EINVAL; > - } else if (!(is_admin || (dst_file->f_mode & FMODE_WRITE))) { > + } else if (!allow_file_dedupe(dst_file)) { > info->status = -EINVAL; > } else if (file->f_path.mnt != dst_file->f_path.mnt) { > info->status = -EXDEV; > -- > 2.15.1 > > -- > To unsubscribe from this list: send the line "unsubscribe linux-xfs" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html ^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH v3 1/2] vfs: allow dedupe of user owned read-only files 2018-06-07 18:17 ` Darrick J. Wong @ 2018-06-07 20:45 ` Mark Fasheh 0 siblings, 0 replies; 5+ messages in thread From: Mark Fasheh @ 2018-06-07 20:45 UTC (permalink / raw) To: Darrick J. Wong Cc: Al Viro, linux-fsdevel, linux-btrfs, linux-xfs, Adam Borowski, David Sterba Hi Darrick, On Thu, Jun 07, 2018 at 11:17:51AM -0700, Darrick J. Wong wrote: > Looks ok, but could you please update the manpage for > ioctl_fideduperange to elaborate on when userspace can expect EPERM? > > Acked-by: Darrick J. Wong <darrick.wong@oracle.com> Yes, good idea. I can handle that. Thanks, --Mark ^ permalink raw reply [flat|nested] 5+ messages in thread
* [PATCH v3 2/2] vfs: dedupe should return EPERM if permission is not granted 2018-06-07 17:38 [PATCH v3 0/2] vfs: better dedupe permission check Mark Fasheh 2018-06-07 17:38 ` [PATCH v3 1/2] vfs: allow dedupe of user owned read-only files Mark Fasheh @ 2018-06-07 17:38 ` Mark Fasheh 1 sibling, 0 replies; 5+ messages in thread From: Mark Fasheh @ 2018-06-07 17:38 UTC (permalink / raw) To: Al Viro Cc: linux-fsdevel, linux-btrfs, linux-xfs, Darrick J . Wong, Adam Borowski, David Sterba, Mark Fasheh Right now we return EINVAL if a process does not have permission to dedupe a file. This was an oversight on my part. EPERM gives a true description of the nature of our error, and EINVAL is already used for the case that the filesystem does not support dedupe. Signed-off-by: Mark Fasheh <mfasheh@suse.de> Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com> Acked-by: David Sterba <dsterba@suse.com> --- fs/read_write.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/fs/read_write.c b/fs/read_write.c index 71e9077f8bc1..7188982e2733 100644 --- a/fs/read_write.c +++ b/fs/read_write.c @@ -2050,7 +2050,7 @@ int vfs_dedupe_file_range(struct file *file, struct file_dedupe_range *same) if (info->reserved) { info->status = -EINVAL; } else if (!allow_file_dedupe(dst_file)) { - info->status = -EINVAL; + info->status = -EPERM; } else if (file->f_path.mnt != dst_file->f_path.mnt) { info->status = -EXDEV; } else if (S_ISDIR(dst->i_mode)) { -- 2.15.1 ^ permalink raw reply related [flat|nested] 5+ messages in thread
end of thread, other threads:[~2018-06-07 20:45 UTC | newest] Thread overview: 5+ messages (download: mbox.gz / follow: Atom feed) -- links below jump to the message on this page -- 2018-06-07 17:38 [PATCH v3 0/2] vfs: better dedupe permission check Mark Fasheh 2018-06-07 17:38 ` [PATCH v3 1/2] vfs: allow dedupe of user owned read-only files Mark Fasheh 2018-06-07 18:17 ` Darrick J. Wong 2018-06-07 20:45 ` Mark Fasheh 2018-06-07 17:38 ` [PATCH v3 2/2] vfs: dedupe should return EPERM if permission is not granted Mark Fasheh
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