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dissect-image: Explicitly remove partitions when done with image

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When closing a loop device, the kernel will asynchronously remove
the probed partitions. This can lead to race conditions where we
try to reuse a partition device that still needs to be removed by
the kernel. To avoid such issues, let's explicitly try to remove
any partitions using BLKPG_DEL_PARTITION when we're done with an
image.

To make sure we don't try to remove partitions when we want them
to remain (e.g. systemd-dissect --mount), we add
dissected_image_relinquish() in a similar vein to loop_device_relinquish()
and decrypted_image_relinquish().
This commit is contained in:
Daan De Meyer 2022-05-18 13:35:21 +02:00 committed by Luca Boccassi
parent af72115412
commit 75d7e04eb4
6 changed files with 75 additions and 5 deletions
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1
src/core/namespace.c
View File

@ -2426,6 +2426,7 @@ int setup_namespace(
}
}
dissected_image_relinquish(dissected_image);
loop_device_relinquish(loop_device);
} else if (root_directory) {

2
src/dissect/dissect.c
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@ -648,6 +648,7 @@ static int action_mount(DissectedImage *m, LoopDevice *d) {
return log_error_errno(r, "Failed to relinquish DM devices: %m");
}
dissected_image_relinquish(m);
loop_device_relinquish(d);
return 0;
}
@ -700,6 +701,7 @@ static int action_copy(DissectedImage *m, LoopDevice *d) {
return log_error_errno(r, "Failed to relinquish DM devices: %m");
}
dissected_image_relinquish(m);
loop_device_relinquish(d);
if (arg_action == ACTION_COPY_FROM) {

2
src/gpt-auto-generator/gpt-auto-generator.c
View File

@ -768,6 +768,8 @@ static int enumerate_partitions(dev_t devnum) {
r = k;
}
dissected_image_relinquish(m);
return r;
}

70
src/shared/dissect-image.c
View File

@ -148,11 +148,45 @@ static void check_partition_flags(
log_debug("Unexpected partition flag %llu set on %s!", bit, node);
}
}
static int ioctl_partition_remove(int fd, const char *name, int nr) {
assert(fd >= 0);
assert(name);
assert(nr > 0);
struct blkpg_partition bp = {
.pno = nr,
};
struct blkpg_ioctl_arg ba = {
.op = BLKPG_DEL_PARTITION,
.data = &bp,
.datalen = sizeof(bp),
};
if (strlen(name) >= sizeof(bp.devname))
return -EINVAL;
strcpy(bp.devname, name);
return RET_NERRNO(ioctl(fd, BLKPG, &ba));
}
#endif
static void dissected_partition_done(DissectedPartition *p) {
static void dissected_partition_done(int fd, DissectedPartition *p) {
assert(fd >= 0);
assert(p);
#if HAVE_BLKID
if (p->node && p->partno > 0 && !p->relinquished) {
int r;
r = ioctl_partition_remove(fd, p->node, p->partno);
if (r < 0)
log_debug_errno(r, "BLKPG_DEL_PARTITION failed, ignoring: %m");
}
#endif
free(p->fstype);
free(p->node);
free(p->label);
@ -332,9 +366,14 @@ int dissect_image(
return -ENOMEM;
*m = (DissectedImage) {
.fd = -1,
.has_init_system = -1,
};
m->fd = fcntl(fd, F_DUPFD_CLOEXEC, 3);
if (m->fd < 0)
return -errno;
r = sd_device_get_sysname(d, &sysname);
if (r < 0)
return log_debug_errno(r, "Failed to get device sysname: %m");
@ -790,10 +829,14 @@ int dissect_image(
* scheme in OS images. */
if (!PARTITION_DESIGNATOR_VERSIONED(designator) ||
strverscmp_improved(m->partitions[designator].label, label) >= 0)
strverscmp_improved(m->partitions[designator].label, label) >= 0) {
r = ioctl_partition_remove(fd, node, nr);
if (r < 0)
log_debug_errno(r, "BLKPG_DEL_PARTITION failed, ignoring: %m");
continue;
}
dissected_partition_done(m->partitions + designator);
dissected_partition_done(fd, m->partitions + designator);
}
if (fstype) {
@ -863,8 +906,12 @@ int dissect_image(
const char *sid, *options = NULL;
/* First one wins */
if (m->partitions[PARTITION_XBOOTLDR].found)
if (m->partitions[PARTITION_XBOOTLDR].found) {
r = ioctl_partition_remove(fd, node, nr);
if (r < 0)
log_debug_errno(r, "BLKPG_DEL_PARTITION failed, ignoring: %m");
continue;
}
sid = blkid_partition_get_uuid(pp);
if (sid)
@ -1178,8 +1225,9 @@ DissectedImage* dissected_image_unref(DissectedImage *m) {
return NULL;
for (PartitionDesignator i = 0; i < _PARTITION_DESIGNATOR_MAX; i++)
dissected_partition_done(m->partitions + i);
dissected_partition_done(m->fd, m->partitions + i);
safe_close(m->fd);
free(m->image_name);
free(m->hostname);
strv_free(m->machine_info);
@ -1189,6 +1237,16 @@ DissectedImage* dissected_image_unref(DissectedImage *m) {
return mfree(m);
}
void dissected_image_relinquish(DissectedImage *m) {
assert(m);
/* Partitions are automatically removed when the underlying loop device is closed. We just need to
* make sure we don't try to remove the partitions early. */
for (PartitionDesignator i = 0; i < _PARTITION_DESIGNATOR_MAX; i++)
m->partitions[i].relinquished = true;
}
static int is_loop_device(const char *path) {
char s[SYS_BLOCK_PATH_MAX("/../loop/")];
struct stat st;
@ -3023,6 +3081,7 @@ int mount_image_privately_interactively(
return log_error_errno(r, "Failed to relinquish DM devices: %m");
}
dissected_image_relinquish(dissected_image);
loop_device_relinquish(d);
*ret_directory = TAKE_PTR(created_dir);
@ -3183,6 +3242,7 @@ int verity_dissect_and_mount(
return log_debug_errno(r, "Failed to relinquish decrypted image: %m");
}
dissected_image_relinquish(dissected_image);
loop_device_relinquish(loop_device);
return 0;

4
src/shared/dissect-image.h
View File

@ -31,6 +31,7 @@ struct DissectedPartition {
char *mount_options;
uint64_t size;
uint64_t offset;
bool relinquished;
};
typedef enum PartitionDesignator {
@ -203,6 +204,8 @@ typedef enum DissectImageFlags {
} DissectImageFlags;
struct DissectedImage {
int fd; /* Backing fd */
bool encrypted:1;
bool has_verity:1; /* verity available in image, but not necessarily used */
bool has_verity_sig:1; /* pkcs#7 signature embedded in image */
@ -258,6 +261,7 @@ int dissect_image_and_warn(int fd, const char *name, const VeritySettings *verit
DissectedImage* dissected_image_unref(DissectedImage *m);
DEFINE_TRIVIAL_CLEANUP_FUNC(DissectedImage*, dissected_image_unref);
void dissected_image_relinquish(DissectedImage *m);
int dissected_image_decrypt(DissectedImage *m, const char *passphrase, const VeritySettings *verity, DissectImageFlags flags, DecryptedImage **ret);
int dissected_image_decrypt_interactively(DissectedImage *m, const char *passphrase, const VeritySettings *verity, DissectImageFlags flags, DecryptedImage **ret);

1
src/sysext/sysext.c
View File

@ -584,6 +584,7 @@ static int merge_subprocess(Hashmap *images, const char *workspace) {
return log_error_errno(r, "Failed to relinquish DM devices: %m");
}
dissected_image_relinquish(m);
loop_device_relinquish(d);
break;
}