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Subject[PATCH] fadvise: avoid EINVAL if user input is valid
The kernel is not required to act on fadvise, so fail silently
and ignore advice as long as it has a valid descriptor and
parameters.

Cc: linux-mm@kvack.org
Cc: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Eric Wong <normalperson@yhbt.net>
---

Of course I wouldn't knowingly call posix_fadvise() on a file in
tmpfs, but a userspace app often doesn't know (nor should it
care) what type of filesystem it's on.

I encountered EINVAL while running the Ruby 1.9.3 test suite on a
stock Debian wheezy installation. Wheezy uses tmpfs for "/tmp" by
default and the test suite creates a temporary file to test the
Ruby wrapper for posix_fadvise() on.

mm/fadvise.c | 19 +++++++------------
1 file changed, 7 insertions(+), 12 deletions(-)

diff --git a/mm/fadvise.c b/mm/fadvise.c
index 469491e0..f9e48dd 100644
--- a/mm/fadvise.c
+++ b/mm/fadvise.c
@@ -43,13 +43,13 @@ SYSCALL_DEFINE(fadvise64_64)(int fd, loff_t offset, loff_t len, int advice)
goto out;
}

- mapping = file->f_mapping;
- if (!mapping || len < 0) {
+ if (len < 0) {
ret = -EINVAL;
goto out;
}

- if (mapping->a_ops->get_xip_mem) {
+ mapping = file->f_mapping;
+ if (!mapping || mapping->a_ops->get_xip_mem) {
switch (advice) {
case POSIX_FADV_NORMAL:
case POSIX_FADV_RANDOM:
@@ -93,10 +93,9 @@ SYSCALL_DEFINE(fadvise64_64)(int fd, loff_t offset, loff_t len, int advice)
spin_unlock(&file->f_lock);
break;
case POSIX_FADV_WILLNEED:
- if (!mapping->a_ops->readpage) {
- ret = -EINVAL;
+ /* ignore the advice if readahead isn't possible (tmpfs) */
+ if (!mapping->a_ops->readpage)
break;
- }

/* First and last PARTIAL page! */
start_index = offset >> PAGE_CACHE_SHIFT;
@@ -106,12 +105,8 @@ SYSCALL_DEFINE(fadvise64_64)(int fd, loff_t offset, loff_t len, int advice)
nrpages = end_index - start_index + 1;
if (!nrpages)
nrpages = ~0UL;
-
- ret = force_page_cache_readahead(mapping, file,
- start_index,
- nrpages);
- if (ret > 0)
- ret = 0;
+
+ force_page_cache_readahead(mapping, file, start_index, nrpages);
break;
case POSIX_FADV_NOREUSE:
break;
--
Eric Wong

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