From 04db8e4fd750dc36ab01f4f61e248b1ebf111bee Mon Sep 17 00:00:00 2001 From: Alexander Potapenko Date: Thu, 15 Sep 2022 17:04:16 +0200 Subject: [PATCH] mm: fs: initialize fsdata passed to write_begin/write_end interface 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 Cc: Alexander Viro Cc: Alexei Starovoitov Cc: Andrey Konovalov Cc: Andrey Konovalov Cc: Andy Lutomirski Cc: Arnd Bergmann Cc: Borislav Petkov Cc: Christoph Hellwig Cc: Christoph Lameter Cc: David Rientjes Cc: Dmitry Vyukov Cc: Eric Biggers Cc: Eric Biggers Cc: Eric Dumazet Cc: Greg Kroah-Hartman Cc: Herbert Xu Cc: Ilya Leoshkevich Cc: Ingo Molnar Cc: Jens Axboe Cc: Joonsoo Kim Cc: Kees Cook Cc: Marco Elver Cc: Mark Rutland Cc: Matthew Wilcox Cc: Michael S. Tsirkin Cc: Pekka Enberg Cc: Peter Zijlstra Cc: Petr Mladek Cc: Stephen Rothwell Cc: Steven Rostedt Cc: Thomas Gleixner Cc: Vasily Gorbik Cc: Vegard Nossum Cc: Vlastimil Babka Signed-off-by: Andrew Morton Signed-off-by: Greg Kroah-Hartman --- 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 9ce03fc5eb32..6077200ea53c 100644 --- a/fs/buffer.c +++ b/fs/buffer.c @@ -2378,7 +2378,7 @@ int generic_cont_expand_simple(struct inode *inode, loff_t size) { struct address_space *mapping = inode->i_mapping; struct page *page; - void *fsdata; + void *fsdata = NULL; int err; err = inode_newsize_ok(inode, size); @@ -2404,7 +2404,7 @@ static int cont_expand_zero(struct file *file, struct address_space *mapping, 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; diff --git a/fs/namei.c b/fs/namei.c index 171e99ad488c..a8c36363e6b1 100644 --- a/fs/namei.c +++ b/fs/namei.c @@ -4847,7 +4847,7 @@ int __page_symlink(struct inode *inode, const char *symname, int len, int nofs) { struct address_space *mapping = inode->i_mapping; struct page *page; - void *fsdata; + void *fsdata = NULL; int err; unsigned int flags = 0; if (nofs) diff --git a/mm/filemap.c b/mm/filemap.c index 471f8091d782..d797b834225a 100644 --- a/mm/filemap.c +++ b/mm/filemap.c @@ -3025,7 +3025,7 @@ ssize_t generic_perform_write(struct file *file, 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, -- 2.20.1