| Message ID | 20180518215727.26418-2-mfasheh@suse.de (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On Fri, May 18, 2018 at 02:57:26PM -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> > --- > 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 c4eabbfc90df..cbea4ce58ad1 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 int allow_file_dedupe(struct file *file) Shouldn't this return bool? It's a predicate, after all... --D > +{ > + if (capable(CAP_SYS_ADMIN)) > + return 1; > + if (file->f_mode & FMODE_WRITE) > + return 1; > + if (uid_eq(current_fsuid(), file_inode(file)->i_uid)) > + return 1; > + if (!inode_permission(file_inode(file), MAY_WRITE)) > + return 1; > + return 0; > +} > + > 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-btrfs" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On Fri, May 18, 2018 at 03:03:38PM -0700, Darrick J. Wong wrote: > > +/* Check whether we are allowed to dedupe the destination file */ > > +static int allow_file_dedupe(struct file *file) > > Shouldn't this return bool? It's a predicate, after all... Yeah that should be bool. Thanks for pointing it out, I'll fix it up in the next round. --Mark -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
diff --git a/fs/read_write.c b/fs/read_write.c index c4eabbfc90df..cbea4ce58ad1 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 int allow_file_dedupe(struct file *file) +{ + if (capable(CAP_SYS_ADMIN)) + return 1; + if (file->f_mode & FMODE_WRITE) + return 1; + if (uid_eq(current_fsuid(), file_inode(file)->i_uid)) + return 1; + if (!inode_permission(file_inode(file), MAY_WRITE)) + return 1; + return 0; +} + 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;
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(-)