Android requires to allow the passing an anonymous inode file descriptor with the restricted functionality - only the mmap operation for the DMA sound buffer (anon_inode:snd-pcm-buffer). Android uses this access mode for the direct EXCLUSIVE sound device access by applications.
This requirement is for the proper SELinux audit.
Signed-off-by: Jaroslav Kysela perex@perex.cz --- include/sound/pcm.h | 2 ++ include/uapi/sound/asound.h | 3 +++ sound/core/pcm_native.c | 36 +++++++++++++++++++++++++++++++++--- 3 files changed, 38 insertions(+), 3 deletions(-)
diff --git a/include/sound/pcm.h b/include/sound/pcm.h index b79ffaa0241d..55b95476d15e 100644 --- a/include/sound/pcm.h +++ b/include/sound/pcm.h @@ -227,6 +227,7 @@ struct snd_pcm_ops { struct snd_pcm_file { struct snd_pcm_substream *substream; int no_compat_mmap; + unsigned int perm; /* file descriptor permissions */ unsigned int user_pversion; /* supported protocol version */ };
@@ -537,6 +538,7 @@ struct snd_pcm { * Registering */
+extern const struct file_operations snd_pcm_f_op_buffer; extern const struct file_operations snd_pcm_f_ops[2];
int snd_pcm_new(struct snd_card *card, const char *id, int device, diff --git a/include/uapi/sound/asound.h b/include/uapi/sound/asound.h index ebc17d5a3490..b0270d07cf4e 100644 --- a/include/uapi/sound/asound.h +++ b/include/uapi/sound/asound.h @@ -571,6 +571,9 @@ enum { #define SNDRV_CHMAP_PHASE_INVERSE (0x01 << 16) #define SNDRV_CHMAP_DRIVER_SPEC (0x02 << 16)
+#define SNDRV_PCM_PERM_MODE_FULL 0 /* full access - no restrictions */ +#define SNDRV_PCM_PERM_MODE_BUFFER 1 /* allow to export only sound buffer through mmap */ + #define SNDRV_PCM_IOCTL_PVERSION _IOR('A', 0x00, int) #define SNDRV_PCM_IOCTL_INFO _IOR('A', 0x01, struct snd_pcm_info) #define SNDRV_PCM_IOCTL_TSTAMP _IOW('A', 0x02, int) diff --git a/sound/core/pcm_native.c b/sound/core/pcm_native.c index bb14658e4482..7a21a2335a8d 100644 --- a/sound/core/pcm_native.c +++ b/sound/core/pcm_native.c @@ -2502,6 +2502,7 @@ static int snd_pcm_open_file(struct file *file, return -ENOMEM; } pcm_file->substream = substream; + pcm_file->perm = 0; if (substream->ref_count == 1) substream->pcm_release = pcm_release_private; file->private_data = pcm_file; @@ -2894,17 +2895,30 @@ static int snd_pcm_anonymous_dup(struct file *file, int fd, err, perm, flags; struct file *nfile; struct snd_pcm *pcm = substream->pcm; + struct snd_pcm_file *pcm_file; + const char *aname; + const struct file_operations *f_op;
if (get_user(perm, arg)) return -EFAULT; - if (perm < 0) - return -EPERM; + switch (perm) { + case SNDRV_PCM_PERM_MODE_FULL: + aname = "snd-pcm"; + f_op = file->f_op; + break; + case SNDRV_PCM_PERM_MODE_BUFFER: + aname = "snd-pcm-buf"; + f_op = &snd_pcm_f_op_buffer; + break; + default: + return -EINVAL; + } flags = file->f_flags & (O_ACCMODE | O_NONBLOCK); flags |= O_APPEND | O_CLOEXEC; fd = get_unused_fd_flags(flags); if (fd < 0) return fd; - nfile = anon_inode_getfile("snd-pcm", file->f_op, NULL, flags); + nfile = anon_inode_getfile(aname, f_op, NULL, flags); if (IS_ERR(nfile)) { put_unused_fd(fd); return PTR_ERR(nfile); @@ -2922,6 +2936,8 @@ static int snd_pcm_anonymous_dup(struct file *file, err = snd_pcm_open_file(nfile, substream->pcm, substream->stream, substream->number); if (err >= 0) { + pcm_file = nfile->private_data; + pcm_file->perm = perm; put_user(fd, arg); return 0; } @@ -3295,6 +3311,9 @@ static int snd_pcm_mmap_status(struct snd_pcm_substream *substream, struct file struct vm_area_struct *area) { long size; + struct snd_pcm_file *pcm_file = file->private_data; + if (pcm_file->perm != SNDRV_PCM_PERM_MODE_FULL) + return -EPERM; if (!(area->vm_flags & VM_READ)) return -EINVAL; size = area->vm_end - area->vm_start; @@ -3331,6 +3350,9 @@ static int snd_pcm_mmap_control(struct snd_pcm_substream *substream, struct file struct vm_area_struct *area) { long size; + struct snd_pcm_file *pcm_file = file->private_data; + if (pcm_file->perm != SNDRV_PCM_PERM_MODE_FULL) + return -EPERM; if (!(area->vm_flags & VM_READ)) return -EINVAL; size = area->vm_end - area->vm_start; @@ -3738,6 +3760,14 @@ static unsigned long snd_pcm_get_unmapped_area(struct file *file, * Register section */
+const struct file_operations snd_pcm_f_op_buffer = { + .owner = THIS_MODULE, + .release = snd_pcm_release, + .llseek = no_llseek, + .mmap = snd_pcm_mmap, + .get_unmapped_area = snd_pcm_get_unmapped_area +}; + const struct file_operations snd_pcm_f_ops[2] = { { .owner = THIS_MODULE,