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libmout: Reuse loop device safely 

Add a safety check to mnt_context_setup_loopdev(). Only a loop device with equal
offset and sizelimit will be reused. If any overlapping loop device exists,
MNT_ERR_LOOPOVERLAP is returned.

Signed-off-by: Stanislav Brabec <sbrabec@suse.cz>
This commit is contained in:
Stanislav Brabec 2016-07-14 15:29:44 +02:00 committed by Karel Zak
parent 211e1d4609
commit 8efad715b9
1 changed files with 52 additions and 13 deletions
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65
libmount/src/context_loopdev.c
View File

@ -215,23 +215,62 @@ int mnt_context_setup_loopdev(struct libmnt_context *cxt)
* mechanism to detect it. To prevent data corruption, the same loop
* device has to be recycled.
*/
rc = loopcxt_init(&lc, 0);
if (rc)
goto done_no_deinit;
if (backing_file && !(loopcxt_find_by_backing_file(&lc,
backing_file, offset, sizelimit, LOOPDEV_FL_OFFSET))) {
DBG(LOOP, ul_debugobj(cxt, "using existing loop device %s",
if (backing_file) {
rc = loopcxt_init(&lc, 0);
if (rc)
goto done_no_deinit;
rc = loopcxt_find_by_backing_file(&lc,
backing_file, offset, sizelimit,
LOOPDEV_FL_OFFSET | LOOPDEV_FL_SIZELIMIT);
if (rc < 0)
goto done;
if (rc == 0) {
uint32_t lc_encrypt_type;
DBG(LOOP, ul_debugobj(cxt, "using existing loop device %s",
loopcxt_get_device(&lc)));
/* Once a loop is initialized RO, there is no
way to change its parameters. */
if (loopcxt_is_readonly(&lc) && !(lo_flags & LO_FLAGS_READ_ONLY)) {
rc = -EROFS;
goto done;
}
/* This is no more supported, but check to be
* safe. */
if (loopcxt_get_encrypt_type(&lc, &lc_encrypt_type)) {
DBG(LOOP, ul_debugobj(cxt, "failed to get crypt type for device %s",
loopcxt_get_device(&lc)));
/* Once a loop is initialized RO, there is no way to safely
mount that file in R/W mode. */
if (loopcxt_is_readonly(&lc) && !(lo_flags & LO_FLAGS_READ_ONLY)) {
rc = -EROFS;
rc = -MNT_ERR_LOOPDEV;
goto done;
}
if (lc_encrypt_type != LO_CRYPT_NONE) {
DBG(LOOP, ul_debugobj(cxt, "encryption no longer supported for device %s",
loopcxt_get_device(&lc)));
rc = -MNT_ERR_LOOPOVERLAP;
goto done;
}
goto success;
}
loopcxt_deinit(&lc);
/* No existing loop device matches. Now we need to
* check that no loop device overlaps our target range
* inside the backing file. */
rc = loopcxt_init(&lc, 0);
if (rc)
goto done_no_deinit;
rc = loopcxt_check_conflict(&lc,
backing_file, offset, sizelimit);
if (rc < 0)
goto done;
if (rc == 0) {
rc = -MNT_ERR_LOOPOVERLAP;
goto done;
}
goto success;
loopcxt_deinit(&lc);
}
loopcxt_deinit(&lc);
rc = loopcxt_init(&lc, 0);
if (rc)