bfs: add sanity check at bfs_fill_super()

syzbot is reporting too large memory allocation at bfs_fill_super() [1].
Since file system image is corrupted such that bfs_sb->s_start == 0,
bfs_fill_super() is trying to allocate 8MB of continuous memory. Fix
this by adding a sanity check on bfs_sb->s_start, __GFP_NOWARN and
printf().

[1] https://syzkaller.appspot.com/bug?id=16a87c236b951351374a84c8a32f40edbc034e96

Link: http://lkml.kernel.org/r/1525862104-3407-1-git-send-email-penguin-kernel@I-love.SAKURA.ne.jp
Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Reported-by: syzbot <syzbot+71c6b5d68e91149fc8a4@syzkaller.appspotmail.com>
Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
Cc: Tigran Aivazian <aivazian.tigran@gmail.com>
Cc: Matthew Wilcox <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 6 insertions, 3 deletions

diff --git a/fs/bfs/inode.c b/fs/bfs/inode.c
index 9a69392f1fb3..d81c148682e7 100644
--- a/fs/bfs/inode.c
+++ b/fs/bfs/inode.c
@@ -350,7 +350,8 @@ static int bfs_fill_super(struct super_block *s, void *data, int silent)
 
         s->s_magic = BFS_MAGIC;
 
-        if (le32_to_cpu(bfs_sb->s_start) > le32_to_cpu(bfs_sb->s_end)) {
+        if (le32_to_cpu(bfs_sb->s_start) > le32_to_cpu(bfs_sb->s_end) ||
+            le32_to_cpu(bfs_sb->s_start) < BFS_BSIZE) {
                 printf("Superblock is corrupted\n");
                 goto out1;
         }
@@ -359,9 +360,11 @@ static int bfs_fill_super(struct super_block *s, void *data, int silent)
                                         sizeof(struct bfs_inode)
                                         + BFS_ROOT_INO - 1;
         imap_len = (info->si_lasti / 8) + 1;
-        info->si_imap = kzalloc(imap_len, GFP_KERNEL);
-        if (!info->si_imap)
+        info->si_imap = kzalloc(imap_len, GFP_KERNEL | __GFP_NOWARN);
+        if (!info->si_imap) {
+                printf("Cannot allocate %u bytes\n", imap_len);
                 goto out1;
+        }
         for (i = 0; i < BFS_ROOT_INO; i++)
                 set_bit(i, info->si_imap);