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[B,4/7] btrfs: extent_io: do extra check for extent buffer read write functions

Message ID 20201030152803.66033-5-mfo@canonical.com
State New
Headers show
Series None | expand

Commit Message

Mauricio Faria de Oliveira Oct. 30, 2020, 3:27 p.m. UTC
From: Qu Wenruo <wqu@suse.com>

BugLink: https://bugs.launchpad.net/bugs/1902254

Although we have start, len check for extent buffer reader/write (e.g.
read_extent_buffer()), these checks have limitations:

- No overflow check
  Values like start = 1024 len = -1024 can still pass the basic
   (start + len) > eb->len check.

- Checks are not consistent
  For read_extent_buffer() we only check (start + len) against eb->len.
  While for memcmp_extent_buffer() we also check start against eb->len.

- Different error reporting mechanism
  We use WARN() in read_extent_buffer() but BUG() in
  memcpy_extent_buffer().

- Still modify memory if the request is obviously wrong
  In read_extent_buffer() even we find (start + len) > eb->len, we still
  call memset(dst, 0, len), which can easily cause memory access error
  if start + len overflows.

To address above problems, this patch creates a new common function to
check such access, check_eb_range().

- Add overflow check
  This function checks start, start + len against eb->len and overflow
  check.

- Unified checks

- Unified error reports
  Will call WARN() if CONFIG_BTRFS_DEBUG is configured.
  And also do btrfs_warn() message for non-debug build.

- Exit ASAP if check fails
  No more possible memory corruption.

- Add extra comment for @start @len used in those functions as it's
  sometimes confused with the logical addressing instead of a range
  inside the eb space

Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=202817
[ Inspired by above report, the report itself is already addressed ]
Reviewed-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: Qu Wenruo <wqu@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
[ use check_add_overflow ]
Signed-off-by: David Sterba <dsterba@suse.com>
(backported from commit f98b6215d7d1cda6ac552b7bc58a6ad092aa517c)
[mfo: backport:
 - hunk 1: new hunk to include 'overflow.h' for check_add_overflow().
 - hunks 8/9 (orig 7/8): refresh lines w/ function signature w/ 'extent_buffer':
   - commit 2b48966a4da4 ("btrfs: constify extent_buffer in the API functions")]
Signed-off-by: Mauricio Faria de Oliveira <mfo@canonical.com>
---
 fs/btrfs/extent_io.c | 85 +++++++++++++++++++++++++-------------------
 1 file changed, 48 insertions(+), 37 deletions(-)
diff mbox series

Patch

diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c
index 44afc39b2fd4..f0c147d35ee9 100644
--- a/fs/btrfs/extent_io.c
+++ b/fs/btrfs/extent_io.c
@@ -12,6 +12,7 @@ 
 #include <linux/pagevec.h>
 #include <linux/prefetch.h>
 #include <linux/cleancache.h>
+#include <linux/overflow.h>
 #include "extent_io.h"
 #include "extent_map.h"
 #include "ctree.h"
@@ -5456,6 +5457,36 @@  int read_extent_buffer_pages(struct extent_io_tree *tree,
 	return ret;
 }
 
+static bool report_eb_range(const struct extent_buffer *eb, unsigned long start,
+			    unsigned long len)
+{
+	btrfs_warn(eb->fs_info,
+		"access to eb bytenr %llu len %lu out of range start %lu len %lu",
+		eb->start, eb->len, start, len);
+	WARN_ON(IS_ENABLED(CONFIG_BTRFS_DEBUG));
+
+	return true;
+}
+
+/*
+ * Check if the [start, start + len) range is valid before reading/writing
+ * the eb.
+ * NOTE: @start and @len are offset inside the eb, not logical address.
+ *
+ * Caller should not touch the dst/src memory if this function returns error.
+ */
+static inline int check_eb_range(const struct extent_buffer *eb,
+				 unsigned long start, unsigned long len)
+{
+	unsigned long offset;
+
+	/* start, start + len should not go beyond eb->len nor overflow */
+	if (unlikely(check_add_overflow(start, len, &offset) || offset > eb->len))
+		return report_eb_range(eb, start, len);
+
+	return false;
+}
+
 void read_extent_buffer(const struct extent_buffer *eb, void *dstv,
 			unsigned long start, unsigned long len)
 {
@@ -5466,12 +5497,8 @@  void read_extent_buffer(const struct extent_buffer *eb, void *dstv,
 	char *dst = (char *)dstv;
 	unsigned long i = start >> PAGE_SHIFT;
 
-	if (start + len > eb->len) {
-		WARN(1, KERN_ERR "btrfs bad mapping eb start %llu len %lu, wanted %lu %lu\n",
-		     eb->start, eb->len, start, len);
-		memset(dst, 0, len);
+	if (check_eb_range(eb, start, len))
 		return;
-	}
 
 	offset = offset_in_page(start);
 
@@ -5578,8 +5605,8 @@  int memcmp_extent_buffer(const struct extent_buffer *eb, const void *ptrv,
 	unsigned long i = start >> PAGE_SHIFT;
 	int ret = 0;
 
-	WARN_ON(start > eb->len);
-	WARN_ON(start + len > eb->start + eb->len);
+	if (check_eb_range(eb, start, len))
+		return -EINVAL;
 
 	offset = offset_in_page(start);
 
@@ -5632,8 +5659,8 @@  void write_extent_buffer(struct extent_buffer *eb, const void *srcv,
 	char *src = (char *)srcv;
 	unsigned long i = start >> PAGE_SHIFT;
 
-	WARN_ON(start > eb->len);
-	WARN_ON(start + len > eb->start + eb->len);
+	if (check_eb_range(eb, start, len))
+		return;
 
 	offset = offset_in_page(start);
 
@@ -5661,8 +5688,8 @@  void memzero_extent_buffer(struct extent_buffer *eb, unsigned long start,
 	char *kaddr;
 	unsigned long i = start >> PAGE_SHIFT;
 
-	WARN_ON(start > eb->len);
-	WARN_ON(start + len > eb->start + eb->len);
+	if (check_eb_range(eb, start, len))
+		return;
 
 	offset = offset_in_page(start);
 
@@ -5705,6 +5732,10 @@  void copy_extent_buffer(struct extent_buffer *dst, struct extent_buffer *src,
 	char *kaddr;
 	unsigned long i = dst_offset >> PAGE_SHIFT;
 
+	if (check_eb_range(dst, dst_offset, len) ||
+	    check_eb_range(src, src_offset, len))
+		return;
+
 	WARN_ON(src->len != dst_len);
 
 	offset = offset_in_page(dst_offset);
@@ -5932,25 +5963,15 @@  static void copy_pages(struct page *dst_page, struct page *src_page,
 void memcpy_extent_buffer(struct extent_buffer *dst, unsigned long dst_offset,
 			   unsigned long src_offset, unsigned long len)
 {
-	struct btrfs_fs_info *fs_info = dst->fs_info;
 	size_t cur;
 	size_t dst_off_in_page;
 	size_t src_off_in_page;
 	unsigned long dst_i;
 	unsigned long src_i;
 
-	if (src_offset + len > dst->len) {
-		btrfs_err(fs_info,
-			"memmove bogus src_offset %lu move len %lu dst len %lu",
-			 src_offset, len, dst->len);
-		BUG();
-	}
-	if (dst_offset + len > dst->len) {
-		btrfs_err(fs_info,
-			"memmove bogus dst_offset %lu move len %lu dst len %lu",
-			 dst_offset, len, dst->len);
-		BUG();
-	}
+	if (check_eb_range(dst, dst_offset, len) ||
+	    check_eb_range(dst, src_offset, len))
+		return;
 
 	while (len > 0) {
 		dst_off_in_page = offset_in_page(dst_offset);
@@ -5976,7 +5997,6 @@  void memcpy_extent_buffer(struct extent_buffer *dst, unsigned long dst_offset,
 void memmove_extent_buffer(struct extent_buffer *dst, unsigned long dst_offset,
 			   unsigned long src_offset, unsigned long len)
 {
-	struct btrfs_fs_info *fs_info = dst->fs_info;
 	size_t cur;
 	size_t dst_off_in_page;
 	size_t src_off_in_page;
@@ -5985,18 +6005,9 @@  void memmove_extent_buffer(struct extent_buffer *dst, unsigned long dst_offset,
 	unsigned long dst_i;
 	unsigned long src_i;
 
-	if (src_offset + len > dst->len) {
-		btrfs_err(fs_info,
-			  "memmove bogus src_offset %lu move len %lu len %lu",
-			  src_offset, len, dst->len);
-		BUG();
-	}
-	if (dst_offset + len > dst->len) {
-		btrfs_err(fs_info,
-			  "memmove bogus dst_offset %lu move len %lu len %lu",
-			  dst_offset, len, dst->len);
-		BUG();
-	}
+	if (check_eb_range(dst, dst_offset, len) ||
+	    check_eb_range(dst, src_offset, len))
+		return;
 	if (dst_offset < src_offset) {
 		memcpy_extent_buffer(dst, dst_offset, src_offset, len);
 		return;