diff options
| author | Amir Goldstein <amir73il@gmail.com> | 2020-02-21 16:34:44 +0200 |
|---|---|---|
| committer | Miklos Szeredi <mszeredi@redhat.com> | 2020-03-27 16:51:02 +0100 |
| commit | dfe51d47b7eeb5642ed92558b62eeff558f00eda (patch) | |
| tree | fe0716c7482cdaa3395aa306375c90715ffaf412 /fs/overlayfs/super.c | |
| parent | 4d314f7859dc1925ee28b4d4e74f6f3a80e6f34b (diff) | |
ovl: avoid possible inode number collisions with xino=on
When xino feature is enabled and a real directory inode number overflows
the lower xino bits, we cannot map this directory inode number to a unique
and persistent inode number and we fall back to the real inode st_ino and
overlay st_dev.
The real inode st_ino with high bits may collide with a lower inode number
on overlay st_dev that was mapped using xino.
To avoid possible collision with legitimate xino values, map a non
persistent inode number to a dedicated range in the xino address space.
The dedicated range is created by adding one more bit to the number of
reserved high xino bits. We could have added just one more fsid, but that
would have had the undesired effect of changing persistent overlay inode
numbers on kernel or require more complex xino mapping code.
Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
Diffstat (limited to 'fs/overlayfs/super.c')
| -rw-r--r-- | fs/overlayfs/super.c | 13 |
1 files changed, 8 insertions, 5 deletions
diff --git a/fs/overlayfs/super.c b/fs/overlayfs/super.c index 1f1d40fc5e33..53dd094f970e 100644 --- a/fs/overlayfs/super.c +++ b/fs/overlayfs/super.c @@ -1483,7 +1483,8 @@ static int ovl_get_layers(struct super_block *sb, struct ovl_fs *ofs, * free high bits in underlying fs to hold the unique fsid. * If overlayfs does encounter underlying inodes using the high xino * bits reserved for fsid, it emits a warning and uses the original - * inode number. + * inode number or a non persistent inode number allocated from a + * dedicated range. */ if (ofs->numfs - !ofs->upper_mnt == 1) { if (ofs->config.xino == OVL_XINO_ON) @@ -1494,11 +1495,13 @@ static int ovl_get_layers(struct super_block *sb, struct ovl_fs *ofs, } else if (ofs->config.xino == OVL_XINO_ON && ofs->xino_mode < 0) { /* * This is a roundup of number of bits needed for encoding - * fsid, where fsid 0 is reserved for upper fs even with - * lower only overlay. + * fsid, where fsid 0 is reserved for upper fs (even with + * lower only overlay) +1 extra bit is reserved for the non + * persistent inode number range that is used for resolving + * xino lower bits overflow. */ - BUILD_BUG_ON(ilog2(OVL_MAX_STACK) > 31); - ofs->xino_mode = ilog2(ofs->numfs - 1) + 1; + BUILD_BUG_ON(ilog2(OVL_MAX_STACK) > 30); + ofs->xino_mode = ilog2(ofs->numfs - 1) + 2; } if (ofs->xino_mode > 0) { |