fs/minix: check return value of sb_getblk()

Patch series "fs/minix: fix syzbot bugs and set s_maxbytes".

This series fixes all syzbot bugs in the minix filesystem:

	KASAN: null-ptr-deref Write in get_block
	KASAN: use-after-free Write in get_block
	KASAN: use-after-free Read in get_block
	WARNING in inc_nlink
	KMSAN: uninit-value in get_block
	WARNING in drop_nlink

It also fixes the minix filesystem to set s_maxbytes correctly, so that
userspace sees the correct behavior when exceeding the max file size.

This patch (of 6):

sb_getblk() can fail, so check its return value.

This fixes a NULL pointer dereference.

Originally from Qiujun Huang.

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Reported-by: syzbot+4a88b2b9dc280f47baf4@syzkaller.appspotmail.com
Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Cc: Qiujun Huang <anenbupt@gmail.com>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: <stable@vger.kernel.org>
Link: http://lkml.kernel.org/r/20200628060846.682158-1-ebiggers@kernel.org
Link: http://lkml.kernel.org/r/20200628060846.682158-2-ebiggers@kernel.org
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/fs/minix/itree_common.c b/fs/minix/itree_common.c
index 043c3fd..4461487 100644 (file)
--- a/fs/minix/itree_common.c
+++ b/fs/minix/itree_common.c
@@ -75,6 +75,7 @@ static int alloc_branch(struct inode *inode,
        int n = 0;
        int i;
        int parent = minix_new_block(inode);
+       int err = -ENOSPC;
 
        branch[0].key = cpu_to_block(parent);
        if (parent) for (n = 1; n < num; n++) {
@@ -85,6 +86,11 @@ static int alloc_branch(struct inode *inode,
                        break;
                branch[n].key = cpu_to_block(nr);
                bh = sb_getblk(inode->i_sb, parent);
+               if (!bh) {
+                       minix_free_block(inode, nr);
+                       err = -ENOMEM;
+                       break;
+               }
                lock_buffer(bh);
                memset(bh->b_data, 0, bh->b_size);
                branch[n].bh = bh;
@@ -103,7 +109,7 @@ static int alloc_branch(struct inode *inode,
                bforget(branch[i].bh);
        for (i = 0; i < n; i++)
                minix_free_block(inode, block_to_cpu(branch[i].key));
-       return -ENOSPC;
+       return err;
 }
 
 static inline int splice_branch(struct inode *inode,