[PATCH] Test for sb_getblk return value

This patch adds tests for the return value of sb_getblk() in the ext2/3
filesystems.  In fs/buffer.c it is stated that the getblk() function never
fails.  However, it does can return NULL in some situations due to I/O
errors, which may lead us to NULL pointer dereferences
Signed-off-by: Glauber de Oliveira Costa <glommer@br.ibm.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

fs/ext2/inode.c

@@ -440,6 +440,10 @@ static int ext2_alloc_branch(struct inode *inode,
 		 * the pointer to new one, then send parent to disk.
 		 */
 		bh = sb_getblk(inode->i_sb, parent);
+		if (!bh) {
+			err = -EIO;
+			break;
+		}
 		lock_buffer(bh);
 		memset(bh->b_data, 0, blocksize);
 		branch[n].bh = bh;

fs/ext3/inode.c

@@ -523,7 +523,6 @@ static int ext3_alloc_branch(handle_t *handle, struct inode *inode,
 			if (!nr)
 				break;
 			branch[n].key = cpu_to_le32(nr);
-			keys = n+1;
 
 			/*
 			 * Get buffer_head for parent block, zero it out
@@ -531,6 +530,9 @@ static int ext3_alloc_branch(handle_t *handle, struct inode *inode,
 			 * parent to disk.  
 			 */
 			bh = sb_getblk(inode->i_sb, parent);
+			if (!bh)
+				break;
+			keys = n+1;
 			branch[n].bh = bh;
 			lock_buffer(bh);
 			BUFFER_TRACE(bh, "call get_create_access");
@@ -864,6 +866,10 @@ struct buffer_head *ext3_getblk(handle_t *handle, struct inode * inode,
 	if (!*errp && buffer_mapped(&dummy)) {
 		struct buffer_head *bh;
 		bh = sb_getblk(inode->i_sb, dummy.b_blocknr);
+		if (!bh) {
+			*errp = -EIO;
+			goto err;
+		}
 		if (buffer_new(&dummy)) {
 			J_ASSERT(create != 0);
 			J_ASSERT(handle != 0);
@@ -896,6 +902,7 @@ struct buffer_head *ext3_getblk(handle_t *handle, struct inode * inode,
 		}
 		return bh;
 	}
+err:
 	return NULL;
 }
 

fs/ext3/resize.c

@@ -118,6 +118,8 @@ static struct buffer_head *bclean(handle_t *handle, struct super_block *sb,
 	int err;
 
 	bh = sb_getblk(sb, blk);
+	if (!bh)
+		return ERR_PTR(-EIO);
 	if ((err = ext3_journal_get_write_access(handle, bh))) {
 		brelse(bh);
 		bh = ERR_PTR(err);
@@ -202,6 +204,10 @@ static int setup_new_group_blocks(struct super_block *sb,
 		ext3_debug("update backup group %#04lx (+%d)\n", block, bit);
 
 		gdb = sb_getblk(sb, block);
+		if (!gdb) {
+			err = -EIO;
+			goto exit_bh;
+		}
 		if ((err = ext3_journal_get_write_access(handle, gdb))) {
 			brelse(gdb);
 			goto exit_bh;
@@ -643,6 +649,10 @@ static void update_backups(struct super_block *sb,
 			break;
 
 		bh = sb_getblk(sb, group * bpg + blk_off);
+		if (!bh) {
+			err = -EIO;
+			break;
+		}
 		ext3_debug("update metadata backup %#04lx\n",
 			  (unsigned long)bh->b_blocknr);
 		if ((err = ext3_journal_get_write_access(handle, bh)))