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authorRich Felker <dalias@aerifal.cx>2021-10-19 16:07:14 -0400
committerRich Felker <dalias@aerifal.cx>2021-10-19 16:07:14 -0400
commit3733c831f293b3bbfd0e51faec8ee71112c62c3e (patch)
tree99df9366357c0435191239bc5803308c7af21ca1 /src
parentb76f37fd5625d038141b52184956fb4b7838e9a5 (diff)
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fix struct layout mismatch in sound ioctl time32 fallback conversion
the snd_pcm_mmap_control struct used with SNDRV_PCM_IOCTL_SYNC_PTR was mistakenly defined in the kernel uapi with "before u32" padding both before and after the first u32 member. our conversion between the modern struct and the legacy time32 struct was written without awareness of that mistake, and assumed the time64 version of the struct was the intended form with padding to match the layout on 64-bit archs. as a result, the struct was not converted correctly when running on old kernels, with audio glitches as the likely result. this was discovered thanks to a related bug in the kernel, whereby 32-bit userspace running on a 64-bit kernel also suffered from the types mismatching. the mistaken layout is now the ABI and can't be changed -- or at least making a new ioctl to change it would just result in a worse situation. our conversion here is changed to treat the snd_pcm_mmap_control substruct as two separate substructs at locations dependent on endianness (since the displacement depends on endianness), using the existing conversion framework.
Diffstat (limited to 'src')
-rw-r--r--src/misc/ioctl.c9
1 files changed, 7 insertions, 2 deletions
diff --git a/src/misc/ioctl.c b/src/misc/ioctl.c
index 49282811..35804f02 100644
--- a/src/misc/ioctl.c
+++ b/src/misc/ioctl.c
@@ -6,6 +6,7 @@
#include <stddef.h>
#include <stdint.h>
#include <string.h>
+#include <endian.h>
#include "syscall.h"
#define alignof(t) offsetof(struct { char c; t x; }, x)
@@ -53,7 +54,7 @@ static const struct ioctl_compat_map compat_map[] = {
{ _IOWR('A', 0x23, char[136]), _IOWR('A', 0x23, char[132]), 0, WR, 1, 0 },
{ 0, 0, 4, WR, 1, 0 }, /* snd_pcm_sync_ptr (flags only) */
{ 0, 0, 32, WR, 1, OFFS(8,12,16,24,28) }, /* snd_pcm_mmap_status */
- { 0, 0, 8, WR, 1, OFFS(0,4) }, /* snd_pcm_mmap_control */
+ { 0, 0, 4, WR, 1, 0 }, /* snd_pcm_mmap_control (each member) */
/* VIDIOC_QUERYBUF, VIDIOC_QBUF, VIDIOC_DQBUF, VIDIOC_PREPARE_BUF */
{ _IOWR('V', 9, new_misaligned(68)), _IOWR('V', 9, char[68]), 68, WR, 1, OFFS(20, 24) },
@@ -90,7 +91,11 @@ static void convert_ioctl_struct(const struct ioctl_compat_map *map, char *old,
* if another exception appears this needs changing. */
convert_ioctl_struct(map+1, old, new, dir);
convert_ioctl_struct(map+2, old+4, new+8, dir);
- convert_ioctl_struct(map+3, old+68, new+72, dir);
+ /* snd_pcm_mmap_control, special-cased due to kernel
+ * type definition having been botched. */
+ int adj = BYTE_ORDER==BIG_ENDIAN ? 4 : 0;
+ convert_ioctl_struct(map+3, old+68, new+72+adj, dir);
+ convert_ioctl_struct(map+3, old+72, new+76+3*adj, dir);
return;
}
for (int i=0; i < map->noffs; i++) {