2023-06-19 13:30:28

by Siddh Raman Pant

Subject: [PATCH v2] jfs: jfs_dmap: Validate db_l2nbperpage while mounting

In jfs_dmap.c at line 381, BLKTODMAP is used to get a logical block
number inside dbFree(). db_l2nbperpage, which is the log2 number of
blocks per page, is passed as an argument to BLKTODMAP which uses it
for shifting.

Syzbot reported a shift out-of-bounds crash because db_l2nbperpage is
too big. This happens because the large value is set without any
validation in dbMount() at line 181.

Thus, make sure that db_l2nbperpage is correct while mounting.

Max number of pages = Page size / Min block size
=> log2(Max number of pages) = log2(Page size / Min block size)
= log2(Page size) - log2(Min block size)

=> Max db_l2nbperpage = L2PSIZE - L2MINBLOCKSIZE

Reported-and-tested-by: [email protected]
Closes: https://syzkaller.appspot.com/bug?id=2a70a453331db32ed491f5cbb07e81bf2d225715
Cc: [email protected]
Suggested-by: Dave Kleikamp <[email protected]>
Signed-off-by: Siddh Raman Pant <[email protected]>
---
Changes in v2:
- Fix upper bound as pointed out in v1 by Shaggy.
- Add an explanation for the same in commit message for completeness.

fs/jfs/jfs_dmap.c | 6 ++++++
fs/jfs/jfs_filsys.h | 2 ++
2 files changed, 8 insertions(+)

diff --git a/fs/jfs/jfs_dmap.c b/fs/jfs/jfs_dmap.c
index a3eb1e826947..da6a2bc6bf02 100644
--- a/fs/jfs/jfs_dmap.c
+++ b/fs/jfs/jfs_dmap.c
@@ -178,7 +178,13 @@ int dbMount(struct inode *ipbmap)
dbmp_le = (struct dbmap_disk *) mp->data;
bmp->db_mapsize = le64_to_cpu(dbmp_le->dn_mapsize);
bmp->db_nfree = le64_to_cpu(dbmp_le->dn_nfree);
+
bmp->db_l2nbperpage = le32_to_cpu(dbmp_le->dn_l2nbperpage);
+ if (bmp->db_l2nbperpage > L2PSIZE - L2MINBLOCKSIZE) {
+ err = -EINVAL;
+ goto err_release_metapage;
+ }
+
bmp->db_numag = le32_to_cpu(dbmp_le->dn_numag);
if (!bmp->db_numag) {
err = -EINVAL;
diff --git a/fs/jfs/jfs_filsys.h b/fs/jfs/jfs_filsys.h
index b5d702df7111..33ef13a0b110 100644
--- a/fs/jfs/jfs_filsys.h
+++ b/fs/jfs/jfs_filsys.h
@@ -122,7 +122,9 @@
#define NUM_INODE_PER_IAG INOSPERIAG

#define MINBLOCKSIZE 512
+#define L2MINBLOCKSIZE 9
#define MAXBLOCKSIZE 4096
+#define L2MAXBLOCKSIZE 12
#define MAXFILESIZE ((s64)1 << 52)

#define JFS_LINK_MAX 0xffffffff
--
2.39.2

2023-06-20 17:06:42

by Siddh Raman Pant

Subject: Re: [PATCH v2] jfs: jfs_dmap: Validate db_l2nbperpage while mounting

On Mon, 19 Jun 2023 18:46:44 +0530 I wrote:
> Max number of pages = Page size / Min block size

Sorry for this typo, it should be max number of blocks (per page).

Will fix and send.

Thanks,
Siddh