[PATCH 3.16 048/328] ALSA: memalloc: Don't exceed over the requested size

Ben Hutchings
2018-12-09T22:11:45Z

From: Takashi Iwai <tiwai@suse.de>

commit dfef01e150824b0e6da750cacda8958188d29aea upstream.

snd_dma_alloc_pages_fallback() tries to allocate pages again when the
allocation fails with reduced size. But the first try actually
*increases* the size to power-of-two, which may give back a larger
chunk than the requested size. This confuses the callers, e.g. sgbuf
assumes that the size is equal or less, and it may result in a bad
loop due to the underflow and eventually lead to Oops.

The code of this function seems incorrectly assuming the usage of
get_order(). We need to decrease at first, then align to
power-of-two.

Reported-and-tested-by: he, bo <bo.he@intel.com>
Reported-by: zhang jun <jun.zhang@intel.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
sound/core/memalloc.c | 8 ++------
1 file changed, 2 insertions(+), 6 deletions(-)

--- a/sound/core/memalloc.c
+++ b/sound/core/memalloc.c
@@ -239,16 +239,12 @@ int snd_dma_alloc_pages_fallback(int typ
int err;

while ((err = snd_dma_alloc_pages(type, device, size, dmab)) < 0) {
- size_t aligned_size;
if (err != -ENOMEM)
return err;
if (size <= PAGE_SIZE)
return -ENOMEM;
- aligned_size = PAGE_SIZE << get_order(size);
- if (size != aligned_size)
- size = aligned_size;
- else
- size >>= 1;
+ size >>= 1;
+ size = PAGE_SIZE << get_order(size);
}
if (! dmab->area)
return -ENOMEM;