udf: limit the maximum number of indirect extents in a row

udf_next_aext() just follows extent pointers while extents are marked as
indirect. This can loop forever for corrupted filesystem. Limit number
the of indirect extents we are willing to follow in a row.

[JK: Updated changelog, limit, style]

Signed-off-by: Vegard Nossum <vegard.nossum@oracle.com>
Cc: stable@vger.kernel.org
Cc: Jan Kara <jack@suse.com>
Cc: Quentin Casasnovas <quentin.casasnovas@oracle.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Jan Kara <jack@suse.cz>

diff --git a/fs/udf/inode.c b/fs/udf/inode.c
index 8d0b3ad..566df9b 100644 (file)
--- a/fs/udf/inode.c
+++ b/fs/udf/inode.c
@@ -2047,14 +2047,29 @@ void udf_write_aext(struct inode *inode, struct extent_position *epos,
                epos->offset += adsize;
 }
 
+/*
+ * Only 1 indirect extent in a row really makes sense but allow upto 16 in case
+ * someone does some weird stuff.
+ */
+#define UDF_MAX_INDIR_EXTS 16
+
 int8_t udf_next_aext(struct inode *inode, struct extent_position *epos,
                     struct kernel_lb_addr *eloc, uint32_t *elen, int inc)
 {
        int8_t etype;
+       unsigned int indirections = 0;
 
        while ((etype = udf_current_aext(inode, epos, eloc, elen, inc)) ==
               (EXT_NEXT_EXTENT_ALLOCDECS >> 30)) {
                int block;
+
+               if (++indirections > UDF_MAX_INDIR_EXTS) {
+                       udf_err(inode->i_sb,
+                               "too many indirect extents in inode %lu\n",
+                               inode->i_ino);
+                       return -1;
+               }
+
                epos->block = *eloc;
                epos->offset = sizeof(struct allocExtDesc);
                brelse(epos->bh);