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authorRandy Dunlap <rdunlap@infradead.org>2020-12-18 12:17:16 -0800
committerDave Kleikamp <dave.kleikamp@oracle.com>2020-12-18 15:23:33 -0600
commit3bef198f1b17d1bb89260bad947ef084c0a2d1a6 (patch)
tree16207f33943d800ae976b762f8d5710bed86a92a /fs/jfs
parenta0b96314870f7eff6d15a242cb162dfc46b3c284 (diff)
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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
Diffstat (limited to 'fs/jfs')
-rw-r--r--fs/jfs/jfs_filsys.h1
-rw-r--r--fs/jfs/jfs_mount.c10
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.