[PATCH] ext4: fix a NULL pointer when validating an inode bitmap

["Luís Henriques" <lhenriques@suse.de>]

It's possible to hit a NULL pointer exception while accessing the
sb->s_group_info in ext4_validate_inode_bitmap(), when calling
ext4_get_group_info().

 EXT4-fs (loop0): warning: mounting unchecked fs, running e2fsck is recommended
 EXT4-fs error (device loop0): ext4_clear_blocks:866: inode #32: comm mount: attempt to clear invalid blocks 16777450 len 1
 EXT4-fs error (device loop0): ext4_free_branches:1012: inode #32: comm mount: invalid indirect mapped block 1258291200 (level 1)
 EXT4-fs error (device loop0): ext4_free_branches:1012: inode #32: comm mount: invalid indirect mapped block 7379847 (level 2)
 BUG: kernel NULL pointer dereference, address: 0000000000000000
 ...
 RIP: 0010:ext4_read_inode_bitmap+0x21b/0x5a0
 ...
 Call Trace:
  <TASK>
  ext4_free_inode+0x172/0x5c0
  ext4_evict_inode+0x4a5/0x730
  evict+0xc1/0x1c0
  ext4_setup_system_zone+0x2ea/0x380
  ext4_fill_super+0x249f/0x3910
  ? ext4_reconfigure+0x880/0x880
  ? snprintf+0x49/0x60
  ? ext4_reconfigure+0x880/0x880
  get_tree_bdev+0x169/0x260
  vfs_get_tree+0x16/0x70
  path_mount+0x77d/0xa30
  __x64_sys_mount+0x101/0x140
  do_syscall_64+0x3c/0x80
  entry_SYSCALL_64_after_hwframe+0x46/0xb0

Fix the issue by adding an extra NULL check.  And, while there, also ensure the
right error code (-EFSCORRUPTED) is propagated to user-space.  EUCLEAN is more
informative than ENOMEM.

CC: stable@vger.kernel.org
Link: https://bugzilla.kernel.org/show_bug.cgi?id=216541
Signed-off-by: Luís Henriques <lhenriques@suse.de>
---
 fs/ext4/ext4.h     | 17 ++++++++++-------
 fs/ext4/ialloc.c   |  2 +-
 fs/ext4/indirect.c | 14 ++++++++++++--
 3 files changed, 23 insertions(+), 10 deletions(-)

diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
index 3bf9a6926798..91317f592999 100644
--- a/fs/ext4/ext4.h
+++ b/fs/ext4/ext4.h
@@ -3323,13 +3323,16 @@ static inline
 struct ext4_group_info *ext4_get_group_info(struct super_block *sb,
 					    ext4_group_t group)
 {
-	 struct ext4_group_info **grp_info;
-	 long indexv, indexh;
-	 BUG_ON(group >= EXT4_SB(sb)->s_groups_count);
-	 indexv = group >> (EXT4_DESC_PER_BLOCK_BITS(sb));
-	 indexh = group & ((EXT4_DESC_PER_BLOCK(sb)) - 1);
-	 grp_info = sbi_array_rcu_deref(EXT4_SB(sb), s_group_info, indexv);
-	 return grp_info[indexh];
+	struct ext4_group_info **grp_info;
+	long indexv, indexh;
+
+	BUG_ON(group >= EXT4_SB(sb)->s_groups_count);
+	if (!EXT4_SB(sb)->s_group_info)
+		return NULL;
+	indexv = group >> (EXT4_DESC_PER_BLOCK_BITS(sb));
+	indexh = group & ((EXT4_DESC_PER_BLOCK(sb)) - 1);
+	grp_info = sbi_array_rcu_deref(EXT4_SB(sb), s_group_info, indexv);
+	return grp_info[indexh];
 }
 
 /*
diff --git a/fs/ext4/ialloc.c b/fs/ext4/ialloc.c
index 208b87ce8858..0e8d35d05b69 100644
--- a/fs/ext4/ialloc.c
+++ b/fs/ext4/ialloc.c
@@ -91,7 +91,7 @@ static int ext4_validate_inode_bitmap(struct super_block *sb,
 
 	if (buffer_verified(bh))
 		return 0;
-	if (EXT4_MB_GRP_IBITMAP_CORRUPT(grp))
+	if (!grp || EXT4_MB_GRP_IBITMAP_CORRUPT(grp))
 		return -EFSCORRUPTED;
 
 	ext4_lock_group(sb, block_group);
diff --git a/fs/ext4/indirect.c b/fs/ext4/indirect.c
index 860fc5119009..e5ac5c2363df 100644
--- a/fs/ext4/indirect.c
+++ b/fs/ext4/indirect.c
@@ -148,6 +148,7 @@ static Indirect *ext4_get_branch(struct inode *inode, int depth,
 	struct super_block *sb = inode->i_sb;
 	Indirect *p = chain;
 	struct buffer_head *bh;
+	unsigned int key;
 	int ret = -EIO;
 
 	*err = 0;
@@ -156,9 +157,18 @@ static Indirect *ext4_get_branch(struct inode *inode, int depth,
 	if (!p->key)
 		goto no_block;
 	while (--depth) {
-		bh = sb_getblk(sb, le32_to_cpu(p->key));
+		key = le32_to_cpu(p->key);
+		bh = sb_getblk(sb, key);
 		if (unlikely(!bh)) {
-			ret = -ENOMEM;
+			/*
+			 * sb_getblk() masks different errors by always
+			 * returning NULL.  Let's distinguish at least the case
+			 * where the block is out of range.
+			 */
+			if (key > ext4_blocks_count(EXT4_SB(sb)->s_es))
+				ret = -EFSCORRUPTED;
+			else
+				ret = -ENOMEM;
 			goto failure;
 		}