diff options
authorNick Piggin <npiggin@suse.de>2007-02-20 13:58:08 -0800
committerLinus Torvalds <torvalds@woody.linux-foundation.org>2007-02-20 17:10:15 -0800
commit955eff5acc8b8cd1c7d4eec0229c35eaabe013db (patch)
parentc066332fb15adde1f37d874a67a1f9f7e4206484 (diff)
[PATCH] fs: fix libfs data leak
simple_prepare_write leaks uninitialised kernel data. This happens because the it leaves an uninitialised "hole" over the part of the page that the write is expected to go to. This is fine, but it then marks the page uptodate, which means a concurrent read can come in and copy the uninitialised memory into userspace before it written to. Fix it by simply marking it uptodate in simple_commit_write instead, after the hole has been filled in. This could theoretically break an fs that uses simple_prepare_write and not simple_commit_write, and that relies on the incorrect simple_prepare_write behaviour. Luckily, none of those exists in the tree. Signed-off-by: Nick Piggin <npiggin@suse.de> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2 files changed, 8 insertions, 2 deletions
diff --git a/Documentation/filesystems/vfs.txt b/Documentation/filesystems/vfs.txt
index 7737bfd03cf8..ea271f2d3954 100644
--- a/Documentation/filesystems/vfs.txt
+++ b/Documentation/filesystems/vfs.txt
@@ -617,6 +617,11 @@ struct address_space_operations {
In this case the prepare_write will be retried one the lock is
+ Note: the page _must not_ be marked uptodate in this function
+ (or anywhere else) unless it actually is uptodate right now. As
+ soon as a page is marked uptodate, it is possible for a concurrent
+ read(2) to copy it to userspace.
commit_write: If prepare_write succeeds, new data will be copied
into the page and then commit_write will be called. It will
typically update the size of the file (if appropriate) and
diff --git a/fs/libfs.c b/fs/libfs.c
index 7d487047dbb8..cf79196535ec 100644
--- a/fs/libfs.c
+++ b/fs/libfs.c
@@ -335,17 +335,18 @@ int simple_prepare_write(struct file *file, struct page *page,
kunmap_atomic(kaddr, KM_USER0);
- SetPageUptodate(page);
return 0;
int simple_commit_write(struct file *file, struct page *page,
- unsigned offset, unsigned to)
+ unsigned from, unsigned to)
struct inode *inode = page->mapping->host;
loff_t pos = ((loff_t)page->index << PAGE_CACHE_SHIFT) + to;
+ if (!PageUptodate(page))
+ SetPageUptodate(page);
* No need to use i_size_read() here, the i_size
* cannot change under us because we hold the i_mutex.