omfs: fix oops when file metadata is corrupted

A fuzzed fileystem image failed with OMFS when the extent count was
used in a loop without being checked against the max number of extents.
It also provoked a signed division for an array index that was checked
as if unsigned, leading to index by -1.

omfsck will be updated to fix these cases, in the meantime bail out
gracefully.

Reported-by: Eric Sesterhenn <snakebyte@gmx.de>
Signed-off-by: Bob Copeland <me@bobcopeland.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 26 insertions, 7 deletions

diff --git a/fs/omfs/file.c b/fs/omfs/file.c
index 7e2499053e4d..834b2331f6b3 100644
--- a/fs/omfs/file.c
+++ b/fs/omfs/file.c
@@ -26,6 +26,13 @@ static int omfs_sync_file(struct file *file, struct dentry *dentry,
         return err ? -EIO : 0;
 }
 
+static u32 omfs_max_extents(struct omfs_sb_info *sbi, int offset)
+{
+        return (sbi->s_sys_blocksize - offset -
+                sizeof(struct omfs_extent)) /
+                sizeof(struct omfs_extent_entry) + 1;
+}
+
 void omfs_make_empty_table(struct buffer_head *bh, int offset)
 {
         struct omfs_extent *oe = (struct omfs_extent *) &bh->b_data[offset];
@@ -45,6 +52,7 @@ int omfs_shrink_inode(struct inode *inode)
         struct buffer_head *bh;
         u64 next, last;
         u32 extent_count;
+        u32 max_extents;
         int ret;
 
         /* traverse extent table, freeing each entry that is greater
@@ -62,15 +70,18 @@ int omfs_shrink_inode(struct inode *inode)
                 goto out;
 
         oe = (struct omfs_extent *)(&bh->b_data[OMFS_EXTENT_START]);
+        max_extents = omfs_max_extents(sbi, OMFS_EXTENT_START);
 
         for (;;) {
 
-                if (omfs_is_bad(sbi, (struct omfs_header *) bh->b_data, next)) {
-                        brelse(bh);
-                        goto out;
-                }
+                if (omfs_is_bad(sbi, (struct omfs_header *) bh->b_data, next))
+                        goto out_brelse;
 
                 extent_count = be32_to_cpu(oe->e_extent_count);
+
+                if (extent_count > max_extents)
+                        goto out_brelse;
+
                 last = next;
                 next = be64_to_cpu(oe->e_next);
                 entry = &oe->e_entry;
@@ -98,10 +109,14 @@ int omfs_shrink_inode(struct inode *inode)
                 if (!bh)
                         goto out;
                 oe = (struct omfs_extent *) (&bh->b_data[OMFS_EXTENT_CONT]);
+                max_extents = omfs_max_extents(sbi, OMFS_EXTENT_CONT);
         }
         ret = 0;
 out:
         return ret;
+out_brelse:
+        brelse(bh);
+        return ret;
 }
 
 static void omfs_truncate(struct inode *inode)
@@ -154,9 +169,7 @@ static int omfs_grow_extent(struct inode *inode, struct omfs_extent *oe,
                         goto out;
                 }
         }
-        max_count = (sbi->s_sys_blocksize - OMFS_EXTENT_START -
-                sizeof(struct omfs_extent)) /
-                sizeof(struct omfs_extent_entry) + 1;
+        max_count = omfs_max_extents(sbi, OMFS_EXTENT_START);
 
         /* TODO: add a continuation block here */
         if (be32_to_cpu(oe->e_extent_count) > max_count-1)
@@ -225,6 +238,7 @@ static int omfs_get_block(struct inode *inode, sector_t block,
         sector_t next, offset;
         int ret;
         u64 new_block;
+        u32 max_extents;
         int extent_count;
         struct omfs_extent *oe;
         struct omfs_extent_entry *entry;
@@ -238,6 +252,7 @@ static int omfs_get_block(struct inode *inode, sector_t block,
                 goto out;
 
         oe = (struct omfs_extent *)(&bh->b_data[OMFS_EXTENT_START]);
+        max_extents = omfs_max_extents(sbi, OMFS_EXTENT_START);
         next = inode->i_ino;
 
         for (;;) {
@@ -249,6 +264,9 @@ static int omfs_get_block(struct inode *inode, sector_t block,
                 next = be64_to_cpu(oe->e_next);
                 entry = &oe->e_entry;
 
+                if (extent_count > max_extents)
+                        goto out_brelse;
+
                 offset = find_block(inode, entry, block, extent_count, &remain);
                 if (offset > 0) {
                         ret = 0;
@@ -266,6 +284,7 @@ static int omfs_get_block(struct inode *inode, sector_t block,
                 if (!bh)
                         goto out;
                 oe = (struct omfs_extent *) (&bh->b_data[OMFS_EXTENT_CONT]);
+                max_extents = omfs_max_extents(sbi, OMFS_EXTENT_CONT);
         }
         if (create) {
                 ret = omfs_grow_extent(inode, oe, &new_block);