From 90fb702791bf99b959006972e8ee7bb4609f441b Mon Sep 17 00:00:00 2001 From: Linus Torvalds Date: Tue, 29 Sep 2020 17:18:34 -0700 Subject: autofs: use __kernel_write() for the autofs pipe writing autofs got broken in some configurations by commit 13c164b1a186 ("autofs: switch to kernel_write") because there is now an extra LSM permission check done by security_file_permission() in rw_verify_area(). autofs is one if the few places that really does want the much more limited __kernel_write(), because the write is an internal kernel one that shouldn't do any user permission checks (it also doesn't need the file_start_write/file_end_write logic, since it's just a pipe). There are a couple of other cases like that - accounting, core dumping, and splice - but autofs stands out because it can be built as a module. As a result, we need to export this internal __kernel_write() function again. We really don't want any other module to use this, but we don't have a "EXPORT_SYMBOL_FOR_AUTOFS_ONLY()". But we can mark it GPL-only to at least approximate that "internal use only" for licensing. While in this area, make autofs pass in NULL for the file position pointer, since it's always a pipe, and we now use a NULL file pointer for streaming file descriptors (see file_ppos() and commit 438ab720c675: "vfs: pass ppos=NULL to .read()/.write() of FMODE_STREAM files") This effectively reverts commits 9db977522449 ("fs: unexport __kernel_write") and 13c164b1a186 ("autofs: switch to kernel_write"). Fixes: 13c164b1a186 ("autofs: switch to kernel_write") Reported-by: Ondrej Mosnacek Acked-by: Christoph Hellwig Acked-by: Acked-by: Ian Kent Signed-off-by: Linus Torvalds --- fs/read_write.c | 8 ++++++++ 1 file changed, 8 insertions(+) (limited to 'fs/read_write.c') diff --git a/fs/read_write.c b/fs/read_write.c index 5db58b8c78d0..d3428189f36b 100644 --- a/fs/read_write.c +++ b/fs/read_write.c @@ -538,6 +538,14 @@ ssize_t __kernel_write(struct file *file, const void *buf, size_t count, loff_t inc_syscw(current); return ret; } +/* + * This "EXPORT_SYMBOL_GPL()" is more of a "EXPORT_SYMBOL_DONTUSE()", + * but autofs is one of the few internal kernel users that actually + * wants this _and_ can be built as a module. So we need to export + * this symbol for autofs, even though it really isn't appropriate + * for any other kernel modules. + */ +EXPORT_SYMBOL_GPL(__kernel_write); ssize_t kernel_write(struct file *file, const void *buf, size_t count, loff_t *pos) -- cgit