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authorDmitri Monakhov <dmonakhov@openvz.org>2008-03-28 14:15:52 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2008-03-28 14:45:21 -0700
commit5b41e74ad1b0bf7bc51765ae74e5dc564afc3e48 (patch)
treee0edafb1d44154b258e013f745d123326183acbd
parent1d4a788f15302877ff2cb08f22009e290a36a209 (diff)
vfs: fix data leak in nobh_write_end()
Current nobh_write_end() implementation ignore partial writes(copied < len) case if page was fully mapped and simply mark page as Uptodate, which is totally wrong because area [pos+copied, pos+len) wasn't updated explicitly in previous write_begin call. It simply contains garbage from pagecache and result in data leakage. #TEST_CASE_BEGIN: ~~~~~~~~~~~~~~~~ In fact issue triggered by classical testcase open("/mnt/test", O_RDWR|O_CREAT|O_TRUNC, 0666) = 3 ftruncate(3, 409600) = 0 writev(3, [{"a", 1}, {NULL, 4095}], 2) = 1 ##TESTCASE_SOURCE: ~~~~~~~~~~~~~~~~~ #include <stdio.h> #include <stdlib.h> #include <fcntl.h> #include <sys/uio.h> #include <sys/mman.h> #include <errno.h> int main(int argc, char **argv) { int fd, ret; void* p; struct iovec iov[2]; fd = open(argv[1], O_RDWR|O_CREAT|O_TRUNC, 0666); ftruncate(fd, 409600); iov[0].iov_base="a"; iov[0].iov_len=1; iov[1].iov_base=NULL; iov[1].iov_len=4096; ret = writev(fd, iov, sizeof(iov)/sizeof(struct iovec)); printf("writev = %d, err = %d\n", ret, errno); return 0; } ##TESTCASE RESULT: ~~~~~~~~~~~~~~~~~~ [root@ts63 ~]# mount | grep mnt2 /dev/mapper/test on /mnt2 type ext2 (rw,nobh) [root@ts63 ~]# /tmp/writev /mnt2/test writev = 1, err = 0 [root@ts63 ~]# hexdump -C /mnt2/test 00000000 61 65 62 6f 6f 74 00 00 f0 b9 b4 59 3a 00 00 00 |aeboot.....Y:...| 00000010 20 00 00 00 00 00 00 00 21 00 00 00 00 00 00 00 | .......!.......| 00000020 df df df df df df df df df df df df df df df df |................| 00000030 3a 00 00 00 2a 00 00 00 21 00 00 00 00 00 00 00 |:...*...!.......| 00000040 60 c0 8c 00 00 00 00 00 40 4a 8d 00 00 00 00 00 |`.......@J......| 00000050 00 00 00 00 00 00 00 00 41 00 00 00 00 00 00 00 |........A.......| 00000060 74 69 6d 65 20 64 64 20 69 66 3d 2f 64 65 76 2f |time dd if=/dev/| 00000070 6c 6f 6f 70 30 20 20 6f 66 3d 2f 64 65 76 2f 6e |loop0 of=/dev/n| skip.. 00000f50 00 00 00 00 00 00 00 00 31 00 00 00 00 00 00 00 |........1.......| 00000f60 6d 6b 66 73 2e 65 78 74 33 20 2f 64 65 76 2f 76 |mkfs.ext3 /dev/v| 00000f70 7a 76 67 2f 74 65 73 74 20 2d 62 34 30 39 36 00 |zvg/test -b4096.| 00000f80 a0 fe 8c 00 00 00 00 00 21 00 00 00 00 00 00 00 |........!.......| 00000f90 23 31 32 30 35 39 35 30 34 30 34 00 3a 00 00 00 |#1205950404.:...| 00000fa0 20 00 8d 00 00 00 00 00 21 00 00 00 00 00 00 00 | .......!.......| 00000fb0 d0 cf 8c 00 00 00 00 00 10 d0 8c 00 00 00 00 00 |................| 00000fc0 00 00 00 00 00 00 00 00 41 00 00 00 00 00 00 00 |........A.......| 00000fd0 6d 6f 75 6e 74 20 2f 64 65 76 2f 76 7a 76 67 2f |mount /dev/vzvg/| 00000fe0 74 65 73 74 20 20 2f 76 7a 20 2d 6f 20 64 61 74 |test /vz -o dat| 00000ff0 61 3d 77 72 69 74 65 62 61 63 6b 00 00 00 00 00 |a=writeback.....| 00001000 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................| As you can see file's page contains garbage from pagecache instead of zeros. #TEST_CASE_END Attached patch: - Add sanity check BUG_ON in order to prevent incorrect usage by caller, This is function invariant because page can has buffers and in no zero *fadata pointer at the same time. - Always attach buffers to page is it is partial write case. - Always switch back to generic_write_end if page has buffers. This is reasonable because if page already has buffer then generic_write_begin was called previously. Signed-off-by: Dmitri Monakhov <dmonakhov@openvz.org> Reviewed-by: Nick Piggin <npiggin@suse.de> Cc: <stable@kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
-rw-r--r--fs/buffer.c13
1 files changed, 6 insertions, 7 deletions
diff --git a/fs/buffer.c b/fs/buffer.c
index 7ba58386beee..98196327ddf0 100644
--- a/fs/buffer.c
+++ b/fs/buffer.c
@@ -2564,14 +2564,13 @@ int nobh_write_end(struct file *file, struct address_space *mapping,
struct inode *inode = page->mapping->host;
struct buffer_head *head = fsdata;
struct buffer_head *bh;
+ BUG_ON(fsdata != NULL && page_has_buffers(page));
- if (!PageMappedToDisk(page)) {
- if (unlikely(copied < len) && !page_has_buffers(page))
- attach_nobh_buffers(page, head);
- if (page_has_buffers(page))
- return generic_write_end(file, mapping, pos, len,
- copied, page, fsdata);
- }
+ if (unlikely(copied < len) && !page_has_buffers(page))
+ attach_nobh_buffers(page, head);
+ if (page_has_buffers(page))
+ return generic_write_end(file, mapping, pos, len,
+ copied, page, fsdata);
SetPageUptodate(page);
set_page_dirty(page);