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authorLinus Torvalds <torvalds@linux-foundation.org>2020-09-29 17:18:34 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2020-09-29 17:18:34 -0700
commit90fb702791bf99b959006972e8ee7bb4609f441b (patch)
tree85cee49cb2af9379d7b4c58a040621122b1816ac /fs/read_write.c
parentccc1d052eff9f3cfe59d201263903fe1d46c79a5 (diff)
downloadlinux-90fb702791bf99b959006972e8ee7bb4609f441b.tar.bz2
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 <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>
Diffstat (limited to 'fs/read_write.c')
-rw-r--r--fs/read_write.c8
1 files changed, 8 insertions, 0 deletions
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)