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Btrfs: check range early in map_private_extent_buffer

PATCH Wang Sheng-Hui 2 participants 3 messages Sep 24, 2012 – Sep 25, 2012 Btrfs file system

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Wang Sheng-Hui

author
#0 lore raw

Check range early to avoid further check/compute in case of range error.

Signed-off-by Wang Sheng-Hui <[email protected]>
---
 fs/btrfs/extent_io.c |   16 ++++++++--------
 1 files changed, 8 insertions(+), 8 deletions(-)
fs/btrfs/extent_io.c +8 -8
index 4c87847..9250cf5 100644
@@ -4643,6 +4643,14 @@ int map_private_extent_buffer(struct extent_buffer *eb, unsigned long start,
 	unsigned long end_i = (start_offset + start + min_len - 1) >>
 		PAGE_CACHE_SHIFT;
 
+	if (start + min_len > eb->len) {
+		printk(KERN_ERR "btrfs bad mapping eb start %llu len %lu, "
+		       "wanted %lu %lu\n", (unsigned long long)eb->start,
+		       eb->len, start, min_len);
+		WARN_ON(1);
+		return -EINVAL;
+	}
+
 	if (i != end_i)
 		return -EINVAL;
 

@@ -4654,14 +4662,6 @@ int map_private_extent_buffer(struct extent_buffer *eb, unsigned long start,
 		*map_start = ((u64)i << PAGE_CACHE_SHIFT) - start_offset;
 	}
 
-	if (start + min_len > eb->len) {
-		printk(KERN_ERR "btrfs bad mapping eb start %llu len %lu, "
-		       "wanted %lu %lu\n", (unsigned long long)eb->start,
-		       eb->len, start, min_len);
-		WARN_ON(1);
-		return -EINVAL;
-	}
-
 	p = extent_buffer_page(eb, i);
 	kaddr = page_address(p);
 	*map = kaddr + offset;
Signature · 1 line
1.7.1
#1 lore raw
Quoted 16 lines · Wang Sheng-Hui

Check range early to avoid further check/compute in case of range error.

Signed-off-by Wang Sheng-Hui <[email protected]>
---
 fs/btrfs/extent_io.c |   16 ++++++++--------
 1 files changed, 8 insertions(+), 8 deletions(-)
fs/btrfs/extent_io.c +0 -0
index 4c87847..9250cf5 100644
@@ -4643,6 +4643,14 @@ int map_private_extent_buffer(struct extent_buffer *eb, unsigned long start,
 	unsigned long end_i = (start_offset + start + min_len - 1) >>
 		PAGE_CACHE_SHIFT;

fs/btrfs/extent_io.c int map_private_extent_buffer(struct extent_buffer *eb, unsigned long start, · line 4655

Quoted 10 lines
fs/btrfs/extent_io.c +8 -0
+	if (start + min_len > eb->len) {
+		printk(KERN_ERR "btrfs bad mapping eb start %llu len %lu, "
+		       "wanted %lu %lu\n", (unsigned long long)eb->start,
+		       eb->len, start, min_len);
+		WARN_ON(1);
+		return -EINVAL;
+	}
+
 	if (i != end_i)
 		return -EINVAL;

4665 unsigned long i = (start_offset + start) >> PAGE_CACHE_SHIFT;
4666 unsigned long end_i = (start_offset + start + min_len - 1) >>
4667 PAGE_CACHE_SHIFT;

so the check above effectively verifies that

min_len - 1 < PAGE_CACHE_SIZE
AND
is within the same page

The other check

	if (start + min_len > eb->len) {

looks if the requested data do not lie out of the bounds of the extent buffer, where min_len is filled with sizeof(something).

So, both the checks look for corrupted metadata, I don't see the need to swap them.

david

author
#2 lore raw
Quoted 40 lines · David Sterba
Quoted 16 lines · Wang Sheng-Hui

Check range early to avoid further check/compute in case of range error.

Signed-off-by Wang Sheng-Hui <[email protected]>
---
 fs/btrfs/extent_io.c |   16 ++++++++--------
 1 files changed, 8 insertions(+), 8 deletions(-)
fs/btrfs/extent_io.c +0 -0
index 4c87847..9250cf5 100644
@@ -4643,6 +4643,14 @@ int map_private_extent_buffer(struct extent_buffer *eb, unsigned long start,
 	unsigned long end_i = (start_offset + start + min_len - 1) >>
 		PAGE_CACHE_SHIFT;

fs/btrfs/extent_io.c int map_private_extent_buffer(struct extent_buffer *eb, unsigned long start, · line 4655

Quoted 10 lines
fs/btrfs/extent_io.c +8 -0
+	if (start + min_len > eb->len) {
+		printk(KERN_ERR "btrfs bad mapping eb start %llu len %lu, "
+		       "wanted %lu %lu\n", (unsigned long long)eb->start,
+		       eb->len, start, min_len);
+		WARN_ON(1);
+		return -EINVAL;
+	}
+
 	if (i != end_i)
 		return -EINVAL;

4665 unsigned long i = (start_offset + start) >> PAGE_CACHE_SHIFT;
4666 unsigned long end_i = (start_offset + start + min_len - 1) >>
4667 PAGE_CACHE_SHIFT;

so the check above effectively verifies that

min_len - 1 < PAGE_CACHE_SIZE
AND
is within the same page

The other check

Quoted 7 lines
	if (start + min_len > eb->len) {

looks if the requested data do not lie out of the bounds of the extent buffer, where min_len is filled with sizeof(something).

So, both the checks look for corrupted metadata, I don't see the need to swap them.

Reread the code and it really does the check.
Got it. Thanks for your explanation.

Quoted 2 lines

david