From: Alexander Potapenko glider@google.com
commit 1468c6f4558b1bcd92aa0400f2920f9dc7588402 upstream.
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.
Link: https://lkml.kernel.org/r/20220915150417.722975-43-glider@google.com Signed-off-by: Alexander Potapenko glider@google.com Cc: Alexander Viro viro@zeniv.linux.org.uk Cc: Alexei Starovoitov ast@kernel.org Cc: Andrey Konovalov andreyknvl@gmail.com Cc: Andrey Konovalov andreyknvl@google.com Cc: Andy Lutomirski luto@kernel.org Cc: Arnd Bergmann arnd@arndb.de Cc: Borislav Petkov bp@alien8.de Cc: Christoph Hellwig hch@lst.de Cc: Christoph Lameter cl@linux.com Cc: David Rientjes rientjes@google.com Cc: Dmitry Vyukov dvyukov@google.com Cc: Eric Biggers ebiggers@google.com Cc: Eric Biggers ebiggers@kernel.org Cc: Eric Dumazet edumazet@google.com Cc: Greg Kroah-Hartman gregkh@linuxfoundation.org Cc: Herbert Xu herbert@gondor.apana.org.au Cc: Ilya Leoshkevich iii@linux.ibm.com Cc: Ingo Molnar mingo@redhat.com Cc: Jens Axboe axboe@kernel.dk Cc: Joonsoo Kim iamjoonsoo.kim@lge.com Cc: Kees Cook keescook@chromium.org Cc: Marco Elver elver@google.com Cc: Mark Rutland mark.rutland@arm.com Cc: Matthew Wilcox willy@infradead.org Cc: Michael S. Tsirkin mst@redhat.com Cc: Pekka Enberg penberg@kernel.org Cc: Peter Zijlstra peterz@infradead.org Cc: Petr Mladek pmladek@suse.com Cc: Stephen Rothwell sfr@canb.auug.org.au Cc: Steven Rostedt rostedt@goodmis.org Cc: Thomas Gleixner tglx@linutronix.de Cc: Vasily Gorbik gor@linux.ibm.com Cc: Vegard Nossum vegard.nossum@oracle.com Cc: Vlastimil Babka vbabka@suse.cz Signed-off-by: Andrew Morton akpm@linux-foundation.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- fs/buffer.c | 4 ++-- fs/namei.c | 2 +- mm/filemap.c | 2 +- 3 files changed, 4 insertions(+), 4 deletions(-)
--- a/fs/buffer.c +++ b/fs/buffer.c @@ -2329,7 +2329,7 @@ int generic_cont_expand_simple(struct in { struct address_space *mapping = inode->i_mapping; struct page *page; - void *fsdata; + void *fsdata = NULL; int err;
err = inode_newsize_ok(inode, size); @@ -2356,7 +2356,7 @@ static int cont_expand_zero(struct file struct inode *inode = mapping->host; 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; --- a/fs/namei.c +++ b/fs/namei.c @@ -4802,7 +4802,7 @@ int __page_symlink(struct inode *inode, { struct address_space *mapping = inode->i_mapping; struct page *page; - void *fsdata; + void *fsdata = NULL; int err; unsigned int flags = AOP_FLAG_UNINTERRUPTIBLE; if (nofs) --- a/mm/filemap.c +++ b/mm/filemap.c @@ -2719,7 +2719,7 @@ ssize_t generic_perform_write(struct fil 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,