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| author | Randy Dunlap <rdunlap@infradead.org> | 2020-12-18 12:17:16 -0800 |
|---|---|---|
| committer | Dave Kleikamp <dave.kleikamp@oracle.com> | 2020-12-18 15:23:33 -0600 |
| commit | 3bef198f1b17d1bb89260bad947ef084c0a2d1a6 (patch) | |
| tree | 16207f33943d800ae976b762f8d5710bed86a92a | |
| parent | a0b96314870f7eff6d15a242cb162dfc46b3c284 (diff) | |
| download | lwn-3bef198f1b17d1bb89260bad947ef084c0a2d1a6.tar.gz lwn-3bef198f1b17d1bb89260bad947ef084c0a2d1a6.zip | |
JFS: more checks for invalid superblock
syzbot is feeding invalid superblock data to JFS for mount testing.
JFS does not check several of the fields -- just assumes that they
are good since the JFS_MAGIC and version fields are good.
In this case (syzbot reproducer), we have s_l2bsize == 0xda0c,
pad == 0xf045, and s_state == 0x50, all of which are invalid IMO.
Having s_l2bsize == 0xda0c causes this UBSAN warning:
UBSAN: shift-out-of-bounds in fs/jfs/jfs_mount.c:373:25
shift exponent -9716 is negative
s_l2bsize can be tested for correctness. pad can be tested for non-0
and punted. s_state can be tested for its valid values and punted.
Do those 3 tests and if any of them fails, report the superblock as
invalid/corrupt and let fsck handle it.
With this patch, chkSuper() says this when JFS_DEBUG is enabled:
jfs_mount: Mount Failure: superblock is corrupt!
Mount JFS Failure: -22
jfs_mount failed w/return code = -22
The obvious problem with this method is that next week there could
be another syzbot test that uses different fields for invalid values,
this making this like a game of whack-a-mole.
syzkaller link: https://syzkaller.appspot.com/bug?extid=36315852ece4132ec193
Reported-by: syzbot+36315852ece4132ec193@syzkaller.appspotmail.com
Reported-by: kernel test robot <lkp@intel.com> # v2
Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Dave Kleikamp <dave.kleikamp@oracle.com>
Cc: jfs-discussion@lists.sourceforge.net
| -rw-r--r-- | fs/jfs/jfs_filsys.h | 1 | ||||
| -rw-r--r-- | fs/jfs/jfs_mount.c | 10 |
2 files changed, 11 insertions, 0 deletions
diff --git a/fs/jfs/jfs_filsys.h b/fs/jfs/jfs_filsys.h index 1e899298f7f0..b5d702df7111 100644 --- a/fs/jfs/jfs_filsys.h +++ b/fs/jfs/jfs_filsys.h @@ -268,5 +268,6 @@ * fsck() must be run to repair */ #define FM_EXTENDFS 0x00000008 /* file system extendfs() in progress */ +#define FM_STATE_MAX 0x0000000f /* max value of s_state */ #endif /* _H_JFS_FILSYS */ diff --git a/fs/jfs/jfs_mount.c b/fs/jfs/jfs_mount.c index 2935d4c776ec..5d7d7170c03c 100644 --- a/fs/jfs/jfs_mount.c +++ b/fs/jfs/jfs_mount.c @@ -37,6 +37,7 @@ #include <linux/fs.h> #include <linux/buffer_head.h> #include <linux/blkdev.h> +#include <linux/log2.h> #include "jfs_incore.h" #include "jfs_filsys.h" @@ -366,6 +367,15 @@ static int chkSuper(struct super_block *sb) sbi->bsize = bsize; sbi->l2bsize = le16_to_cpu(j_sb->s_l2bsize); + /* check some fields for possible corruption */ + if (sbi->l2bsize != ilog2((u32)bsize) || + j_sb->pad != 0 || + le32_to_cpu(j_sb->s_state) > FM_STATE_MAX) { + rc = -EINVAL; + jfs_err("jfs_mount: Mount Failure: superblock is corrupt!"); + goto out; + } + /* * For now, ignore s_pbsize, l2bfactor. All I/O going through buffer * cache. |