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Message-ID: <20220915150417.722975-43-glider@google.com>
Date: Thu, 15 Sep 2022 17:04:16 +0200
From: Alexander Potapenko <glider@...gle.com>
To: glider@...gle.com
Cc: Alexander Viro <viro@...iv.linux.org.uk>,
Alexei Starovoitov <ast@...nel.org>,
Andrew Morton <akpm@...ux-foundation.org>,
Andrey Konovalov <andreyknvl@...gle.com>,
Andy Lutomirski <luto@...nel.org>,
Arnd Bergmann <arnd@...db.de>, Borislav Petkov <bp@...en8.de>,
Christoph Hellwig <hch@....de>,
Christoph Lameter <cl@...ux.com>,
David Rientjes <rientjes@...gle.com>,
Dmitry Vyukov <dvyukov@...gle.com>,
Eric Biggers <ebiggers@...nel.org>,
Eric Dumazet <edumazet@...gle.com>,
Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
Herbert Xu <herbert@...dor.apana.org.au>,
Ilya Leoshkevich <iii@...ux.ibm.com>,
Ingo Molnar <mingo@...hat.com>, Jens Axboe <axboe@...nel.dk>,
Joonsoo Kim <iamjoonsoo.kim@....com>,
Kees Cook <keescook@...omium.org>,
Marco Elver <elver@...gle.com>,
Mark Rutland <mark.rutland@....com>,
Matthew Wilcox <willy@...radead.org>,
"Michael S. Tsirkin" <mst@...hat.com>,
Pekka Enberg <penberg@...nel.org>,
Peter Zijlstra <peterz@...radead.org>,
Petr Mladek <pmladek@...e.com>,
Stephen Rothwell <sfr@...b.auug.org.au>,
Steven Rostedt <rostedt@...dmis.org>,
Thomas Gleixner <tglx@...utronix.de>,
Vasily Gorbik <gor@...ux.ibm.com>,
Vegard Nossum <vegard.nossum@...cle.com>,
Vlastimil Babka <vbabka@...e.cz>, kasan-dev@...glegroups.com,
linux-mm@...ck.org, linux-arch@...r.kernel.org,
linux-kernel@...r.kernel.org
Subject: [PATCH v7 42/43] mm: fs: initialize fsdata passed to
write_begin/write_end interface
Functions implementing the a_ops->write_end() interface accept the
`void *fsdata` parameter that is supposed to be initialized by the
corresponding a_ops->write_begin() (which accepts `void **fsdata`).
However not all a_ops->write_begin() implementations initialize `fsdata`
unconditionally, so it may get passed uninitialized to a_ops->write_end(),
resulting in undefined behavior.
Fix this by initializing fsdata with NULL before the call to
write_begin(), rather than doing so in all possible a_ops
implementations.
This patch covers only the following cases found by running x86 KMSAN
under syzkaller:
- generic_perform_write()
- cont_expand_zero() and generic_cont_expand_simple()
- page_symlink()
Other cases of passing uninitialized fsdata may persist in the codebase.
Signed-off-by: Alexander Potapenko <glider@...gle.com>
---
Link: https://linux-review.googlesource.com/id/Ie300c21bbe9dea69a730745bd3c6d2720953bf41
---
fs/buffer.c | 4 ++--
fs/namei.c | 2 +-
mm/filemap.c | 2 +-
3 files changed, 4 insertions(+), 4 deletions(-)
diff --git a/fs/buffer.c b/fs/buffer.c
index 55e762a58eb65..e1198f4b28c8f 100644
--- a/fs/buffer.c
+++ b/fs/buffer.c
@@ -2352,7 +2352,7 @@ int generic_cont_expand_simple(struct inode *inode, loff_t size)
struct address_space *mapping = inode->i_mapping;
const struct address_space_operations *aops = mapping->a_ops;
struct page *page;
- void *fsdata;
+ void *fsdata = NULL;
int err;
err = inode_newsize_ok(inode, size);
@@ -2378,7 +2378,7 @@ static int cont_expand_zero(struct file *file, struct address_space *mapping,
const struct address_space_operations *aops = mapping->a_ops;
unsigned int blocksize = i_blocksize(inode);
struct page *page;
- void *fsdata;
+ void *fsdata = NULL;
pgoff_t index, curidx;
loff_t curpos;
unsigned zerofrom, offset, len;
diff --git a/fs/namei.c b/fs/namei.c
index 53b4bc094db23..076ae96ca0b14 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -5088,7 +5088,7 @@ int page_symlink(struct inode *inode, const char *symname, int len)
const struct address_space_operations *aops = mapping->a_ops;
bool nofs = !mapping_gfp_constraint(mapping, __GFP_FS);
struct page *page;
- void *fsdata;
+ void *fsdata = NULL;
int err;
unsigned int flags;
diff --git a/mm/filemap.c b/mm/filemap.c
index 15800334147b3..ada25b9f45ad1 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -3712,7 +3712,7 @@ ssize_t generic_perform_write(struct kiocb *iocb, struct iov_iter *i)
unsigned long offset; /* Offset into pagecache page */
unsigned long bytes; /* Bytes to write to page */
size_t copied; /* Bytes copied from user */
- void *fsdata;
+ void *fsdata = NULL;
offset = (pos & (PAGE_SIZE - 1));
bytes = min_t(unsigned long, PAGE_SIZE - offset,
--
2.37.2.789.g6183377224-goog
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