On 6/20/23 11:47AM, Siddh Raman Pant wrote:

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 blocks per page = Page size / Min block size => log2(Max num_block per page) = log2(Page size / Min block size) = log2(Page size) - log2(Min block size)

=> Max db_l2nbperpage = L2PSIZE - L2MINBLOCKSIZE

Thanks. Applied to jfs-next.

Reported-and-tested-by: syzbot+d2cd27dcf8e04b232eb2@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?id=2a70a453331db32ed491f5cbb07e81bf2d22571... Cc: stable@vger.kernel.org Suggested-by: Dave Kleikamp dave.kleikamp@oracle.com Signed-off-by: Siddh Raman Pant code@siddh.me

---

Changes in v3:

• Fix typo in commit message (number of pages -> number of blocks per page).

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