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Subject[PATCH] vfs: allow FILE_EXTENT_SAME (dedupe_file_range) on a file opened ro
Instead of checking the mode of the file descriptor, let's check whether it
could have been opened rw. This allows fixing intermittent exec failures
when deduping a live system: anyone trying to exec a file currently being
deduped gets ETXTBSY.

Issuing this ioctl on a ro file was already allowed for root/cap.

Tested on btrfs and not-yet-merged xfs, as only them implement this ioctl.

Signed-off-by: Adam Borowski <kilobyte@angband.pl>
---
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 933b53a..df59dc6 100644
--- a/fs/read_write.c
+++ b/fs/read_write.c
@@ -1723,7 +1723,7 @@ 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 (!(is_admin || !inode_permission(dst, MAY_WRITE))) {
info->status = -EINVAL;
} else if (file->f_path.mnt != dst_file->f_path.mnt) {
info->status = -EXDEV;
--
2.8.1
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