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executor: determine the next free loop device #6418

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executor: determine the next free loop device #6418

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31 changes: 27 additions & 4 deletions executor/common_linux.h
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Original file line number Diff line number Diff line change
Expand Up @@ -3032,6 +3032,22 @@ static void reset_loop_device(const char* loopname)

#endif

#if SYZ_EXECUTOR || __NR_syz_read_part_table || __NR_syz_mount_image
static int loopnr;

static int loop_get_free(void)
{
int ctlfd;

ctlfd = open("/dev/loop-control", O_RDWR);
if (ctlfd == -1)
return -1;
loopnr = ioctl(ctlfd, LOOP_CTL_GET_FREE);
close(ctlfd);
return loopnr;
}
#endif

#if SYZ_EXECUTOR || __NR_syz_read_part_table
// syz_read_part_table(size len[img], img ptr[in, compressed_image])
static long syz_read_part_table(volatile unsigned long size, volatile long image)
Expand All @@ -3040,7 +3056,10 @@ static long syz_read_part_table(volatile unsigned long size, volatile long image
int err = 0, res = -1, loopfd = -1;
char loopname[64];

snprintf(loopname, sizeof(loopname), "/dev/loop%llu", procid);
loopnr = loop_get_free();
if (loopnr == -1)
return -1;
snprintf(loopname, sizeof(loopname), "/dev/loop%d", loopnr);
if (setup_loop_device(data, size, loopname, &loopfd) == -1)
return -1;

Expand All @@ -3060,7 +3079,7 @@ static long syz_read_part_table(volatile unsigned long size, volatile long image
res = 0;
// If we managed to parse some partitions, symlink them into our work dir.
for (unsigned long i = 1, j = 0; i < 8; i++) {
snprintf(loopname, sizeof(loopname), "/dev/loop%llup%d", procid, (int)i);
snprintf(loopname, sizeof(loopname), "/dev/loop%dp%d", loopnr, (int)i);
struct stat statbuf;
if (stat(loopname, &statbuf) == 0) {
char linkname[64];
Expand Down Expand Up @@ -3112,10 +3131,14 @@ static long syz_mount_image(

if (need_loop_device) {
int loopfd;

// Some filesystems (e.g. FUSE) do not need a backing device or
// filesystem image.
loopnr = loop_get_free();
if (loopnr == -1)
return -1;
memset(loopname, 0, sizeof(loopname));
snprintf(loopname, sizeof(loopname), "/dev/loop%llu", procid);
snprintf(loopname, sizeof(loopname), "/dev/loop%d", loopnr);
if (setup_loop_device(data, size, loopname, &loopfd) == -1)
return -1;
// If BLK_DEV_WRITE_MOUNTED is set, we won't be able to mount()
Expand Down Expand Up @@ -4850,7 +4873,7 @@ static void reset_loop()
{
#if SYZ_EXECUTOR || __NR_syz_mount_image || __NR_syz_read_part_table
char buf[64];
snprintf(buf, sizeof(buf), "/dev/loop%llu", procid);
snprintf(buf, sizeof(buf), "/dev/loop%d", loopnr);
int loopfd = open(buf, O_RDWR);
if (loopfd != -1) {
ioctl(loopfd, LOOP_CLR_FD, 0);
Expand Down