[Ocfs2-devel] [PATCH v2] ocfs2: don't put and assigning null to bh allocated outside

[Changwei Ge]

From: Changwei Ge <ge.changwei at h3c.com>

ocfs2_read_blocks() and ocfs2_read_blocks_sync() are both used to read
several blocks from disk. Currently, the input argument *bhs* can be
NULL or NOT. It depends on the caller's behavior. If the function fails
in reading blocks from disk, the corresponding bh will be assigned to
NULL and put.

Obviously, above process for non-NULL input bh is not appropriate.
Because the caller doesn't even know its bhs are put and re-assigned.

If buffer head is managed by caller, ocfs2_read_blocks and
ocfs2_read_blocks_sync()  should not evaluate it to NULL. It will
cause caller accessing illegal memory, thus crash.


change from v1:
Fix misuse of bh, which may cause NULL pointer accessing. 

Signed-off-by: Changwei Ge <ge.changwei at h3c.com>
---
 fs/ocfs2/buffer_head_io.c | 77 ++++++++++++++++++++++++++++++++++++-----------
 1 file changed, 59 insertions(+), 18 deletions(-)

diff --git a/fs/ocfs2/buffer_head_io.c b/fs/ocfs2/buffer_head_io.c
index d9ebe11..9f0304f 100644
--- a/fs/ocfs2/buffer_head_io.c
+++ b/fs/ocfs2/buffer_head_io.c
@@ -99,25 +99,34 @@ int ocfs2_write_block(struct ocfs2_super *osb, struct buffer_head *bh,
 	return ret;
 }
 
+/* Caller must provide a bhs[] with all NULL or non-NULL entries, so it
+ * will be easier to handle read failure.
+ */
 int ocfs2_read_blocks_sync(struct ocfs2_super *osb, u64 block,
 			   unsigned int nr, struct buffer_head *bhs[])
 {
 	int status = 0;
 	unsigned int i;
 	struct buffer_head *bh;
+	int new_bh = 0;
 
 	trace_ocfs2_read_blocks_sync((unsigned long long)block, nr);
 
 	if (!nr)
 		goto bail;
 
+	/* Don't put buffer head and re-assign it to NULL if it is allocated
+	 * outside since the caller can't be aware of this alternation!
+	 */
+	new_bh = (bhs[0] == NULL);
+
 	for (i = 0 ; i < nr ; i++) {
 		if (bhs[i] == NULL) {
 			bhs[i] = sb_getblk(osb->sb, block++);
 			if (bhs[i] == NULL) {
 				status = -ENOMEM;
 				mlog_errno(status);
-				goto bail;
+				break;
 			}
 		}
 		bh = bhs[i];
@@ -158,9 +167,26 @@ int ocfs2_read_blocks_sync(struct ocfs2_super *osb, u64 block,
 		submit_bh(REQ_OP_READ, 0, bh);
 	}
 
+read_failure:
 	for (i = nr; i > 0; i--) {
 		bh = bhs[i - 1];
 
+		if (unlikely(status)) {
+			if (new_bh && bh) {
+				/* If middle bh fails, let previous bh
+				 * finish its read and then put it to
+				 * aovoid bh leak
+				 */
+				if (!buffer_jbd(bh))
+					wait_on_buffer(bh);
+				put_bh(bh);
+				bhs[i - 1] = NULL;
+			} else if (bh && buffer_uptodate(bh)) {
+				clear_buffer_uptodate(bh);
+			}
+			continue;
+		}
+
 		/* No need to wait on the buffer if it's managed by JBD. */
 		if (!buffer_jbd(bh))
 			wait_on_buffer(bh);
@@ -170,8 +196,7 @@ int ocfs2_read_blocks_sync(struct ocfs2_super *osb, u64 block,
 			 * so we can safely record this and loop back
 			 * to cleanup the other buffers. */
 			status = -EIO;
-			put_bh(bh);
-			bhs[i - 1] = NULL;
+			goto read_failure;
 		}
 	}
 
@@ -179,6 +204,9 @@ int ocfs2_read_blocks_sync(struct ocfs2_super *osb, u64 block,
 	return status;
 }
 
+/* Caller must provide a bhs[] with all NULL or non-NULL entries, so it
+ * will be easier to handle read failure.
+ */
 int ocfs2_read_blocks(struct ocfs2_caching_info *ci, u64 block, int nr,
 		      struct buffer_head *bhs[], int flags,
 		      int (*validate)(struct super_block *sb,
@@ -188,6 +216,7 @@ int ocfs2_read_blocks(struct ocfs2_caching_info *ci, u64 block, int nr,
 	int i, ignore_cache = 0;
 	struct buffer_head *bh;
 	struct super_block *sb = ocfs2_metadata_cache_get_super(ci);
+	int new_bh = 0;
 
 	trace_ocfs2_read_blocks_begin(ci, (unsigned long long)block, nr, flags);
 
@@ -213,6 +242,11 @@ int ocfs2_read_blocks(struct ocfs2_caching_info *ci, u64 block, int nr,
 		goto bail;
 	}
 
+	/* Don't put buffer head and re-assign it to NULL if it is allocated
+	 * outside since the caller can't be aware of this alternation!
+	 */
+	new_bh = (bhs[0] == NULL);
+
 	ocfs2_metadata_cache_io_lock(ci);
 	for (i = 0 ; i < nr ; i++) {
 		if (bhs[i] == NULL) {
@@ -221,7 +255,8 @@ int ocfs2_read_blocks(struct ocfs2_caching_info *ci, u64 block, int nr,
 				ocfs2_metadata_cache_io_unlock(ci);
 				status = -ENOMEM;
 				mlog_errno(status);
-				goto bail;
+				/* Don't forget to put previous bh! */
+				break;
 			}
 		}
 		bh = bhs[i];
@@ -316,16 +351,27 @@ int ocfs2_read_blocks(struct ocfs2_caching_info *ci, u64 block, int nr,
 		}
 	}
 
-	status = 0;
-
+read_failure:
 	for (i = (nr - 1); i >= 0; i--) {
 		bh = bhs[i];
 
 		if (!(flags & OCFS2_BH_READAHEAD)) {
-			if (status) {
-				/* Clear the rest of the buffers on error */
-				put_bh(bh);
-				bhs[i] = NULL;
+			if (unlikely(status)) {
+				/* Clear the buffers on error including those
+				 * ever succeeded in reading
+				 */
+				if (new_bh && bh) {
+					/* If middle bh fails, let previous bh
+					 * finish its read and then put it to
+					 * aovoid bh leak
+					 */
+					if (!buffer_jbd(bh))
+						wait_on_buffer(bh);
+					put_bh(bh);
+					bhs[i] = NULL;
+				} else if (bh && buffer_uptodate(bh)) {
+					clear_buffer_uptodate(bh);
+				}
 				continue;
 			}
 			/* We know this can't have changed as we hold the
@@ -342,9 +388,7 @@ int ocfs2_read_blocks(struct ocfs2_caching_info *ci, u64 block, int nr,
 				 * for this bh as it's not marked locally
 				 * uptodate. */
 				status = -EIO;
-				put_bh(bh);
-				bhs[i] = NULL;
-				continue;
+				goto read_failure;
 			}
 
 			if (buffer_needs_validate(bh)) {
@@ -354,11 +398,8 @@ int ocfs2_read_blocks(struct ocfs2_caching_info *ci, u64 block, int nr,
 				BUG_ON(buffer_jbd(bh));
 				clear_buffer_needs_validate(bh);
 				status = validate(sb, bh);
-				if (status) {
-					put_bh(bh);
-					bhs[i] = NULL;
-					continue;
-				}
+				if (status)
+					goto read_failure;
 			}
 		}
 
-- 
2.7.4