From: Linus Torvalds torvalds@linux-foundation.org
[ Upstream commit 90fb702791bf99b959006972e8ee7bb4609f441b ]
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 omosnace@redhat.com Acked-by: Christoph Hellwig hch@lst.de Acked-by: Acked-by: Ian Kent raven@themaw.net Signed-off-by: Linus Torvalds torvalds@linux-foundation.org Signed-off-by: Sasha Levin sashal@kernel.org --- fs/autofs/waitq.c | 2 +- fs/read_write.c | 8 ++++++++ 2 files changed, 9 insertions(+), 1 deletion(-)
diff --git a/fs/autofs/waitq.c b/fs/autofs/waitq.c index 74c886f7c51cb..5ced859dac539 100644 --- a/fs/autofs/waitq.c +++ b/fs/autofs/waitq.c @@ -53,7 +53,7 @@ static int autofs_write(struct autofs_sb_info *sbi,
mutex_lock(&sbi->pipe_mutex); while (bytes) { - wr = kernel_write(file, data, bytes, &file->f_pos); + wr = __kernel_write(file, data, bytes, NULL); if (wr <= 0) break; data += wr; diff --git a/fs/read_write.c b/fs/read_write.c index 4fb797822567a..9a5cb9c2f0d46 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)