linux-kernel - [PATCH 4.9 160/212] fs/minix: check return value of sb

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Date:   Thu, 20 Aug 2020 11:22:13 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org,
        syzbot+4a88b2b9dc280f47baf4@...kaller.appspotmail.com,
        Eric Biggers <ebiggers@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Qiujun Huang <anenbupt@...il.com>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: [PATCH 4.9 160/212] fs/minix: check return value of sb_getblk()

From: Eric Biggers <ebiggers@...gle.com>

commit da27e0a0e5f655f0d58d4e153c3182bb2b290f64 upstream.

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@...kaller.appspotmail.com
Signed-off-by: Eric Biggers <ebiggers@...gle.com>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
Cc: Qiujun Huang <anenbupt@...il.com>
Cc: Alexander Viro <viro@...iv.linux.org.uk>
Cc: <stable@...r.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@...ux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 fs/minix/itree_common.c |    8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

--- a/fs/minix/itree_common.c
+++ b/fs/minix/itree_common.c
@@ -74,6 +74,7 @@ static int alloc_branch(struct inode *in
 	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++) {
@@ -84,6 +85,11 @@ static int alloc_branch(struct inode *in
 			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;
@@ -102,7 +108,7 @@ static int alloc_branch(struct inode *in
 		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,