diff options
authorLinus Torvalds <>2020-09-29 17:18:34 -0700
committerGreg Kroah-Hartman <>2020-10-07 08:02:53 +0200
commit5f040ac168f3e680c429a2a68b2f7a46e2c5f4a3 (patch)
parentb06582ae50525d06dfe2888692166ae12f5ff281 (diff)
autofs: use __kernel_write() for the autofs pipe writing
[ 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 <> Acked-by: Christoph Hellwig <> Acked-by: Acked-by: Ian Kent <> Signed-off-by: Linus Torvalds <> Signed-off-by: Sasha Levin <>
2 files changed, 9 insertions, 1 deletions
diff --git a/fs/autofs/waitq.c b/fs/autofs/waitq.c
index 74c886f7c51c..5ced859dac53 100644
--- a/fs/autofs/waitq.c
+++ b/fs/autofs/waitq.c
@@ -53,7 +53,7 @@ static int autofs_write(struct autofs_sb_info *sbi,
while (bytes) {
- wr = kernel_write(file, data, bytes, &file->f_pos);
+ wr = __kernel_write(file, data, bytes, NULL);
if (wr <= 0)
data += wr;
diff --git a/fs/read_write.c b/fs/read_write.c
index 4fb797822567..9a5cb9c2f0d4 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
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.
+ */
ssize_t kernel_write(struct file *file, const void *buf, size_t count,
loff_t *pos)