jfs: jfs_dmap: Validate db_l2nbperpage while mounting

commit 11509910c599cbd04585ec35a6d5e1a0053d84c1 upstream.

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

Reported-and-tested-by: syzbot+d2cd27dcf8e04b232eb2@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?id=2a70a453331db32ed491f5cbb07e81bf2d225715
Cc: stable@vger.kernel.org
Suggested-by: Dave Kleikamp <dave.kleikamp@oracle.com>
Signed-off-by: Siddh Raman Pant <code@siddh.me>
Signed-off-by: Dave Kleikamp <dave.kleikamp@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/fs/jfs/jfs_dmap.c b/fs/jfs/jfs_dmap.c
index a3eb1e82694778e907658fd6ea79f0d8d2eee724..da6a2bc6bf022df6930b5549e237924945f16a53 100644 (file)
--- 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 b5d702df7111a919a79f903ffe5462845deb4bd3..33ef13a0b110826b9c484f5d33cfa23c4a83ded2 100644 (file)
--- 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