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Check the vfs option length is valid before accessing through

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When a VFS option passed to nmount is present but NULL the kernel will
place an empty option in its internal list. This will have a NULL
pointer and a length of 0. When we come to read one of these the kernel
will try to load from the last address of virtual memory. This is
normally invalid so will fault resulting in a kernel panic.

Fix this by checking if the length is valid before dereferencing.

MFC after:	3 days
Sponsored by:	DARPA, AFRL
This commit is contained in:
Andrew Turner 2019-09-27 16:22:28 +00:00
parent 4470d73996
commit 50bb04b750
1 changed files with 2 additions and 2 deletions
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4
sys/kern/vfs_mount.c
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@ -646,7 +646,7 @@ vfs_donmount(struct thread *td, uint64_t fsflags, struct uio *fsoptions)
*/
fstypelen = 0;
error = vfs_getopt(optlist, "fstype", (void **)&fstype, &fstypelen);
if (error || fstype[fstypelen - 1] != '\0') {
if (error || fstypelen <= 0 || fstype[fstypelen - 1] != '\0') {
error = EINVAL;
if (errmsg != NULL)
strncpy(errmsg, "Invalid fstype", errmsg_len);
@ -654,7 +654,7 @@ vfs_donmount(struct thread *td, uint64_t fsflags, struct uio *fsoptions)
}
fspathlen = 0;
error = vfs_getopt(optlist, "fspath", (void **)&fspath, &fspathlen);
if (error || fspath[fspathlen - 1] != '\0') {
if (error || fspathlen <= 0 || fspath[fspathlen - 1] != '\0') {
error = EINVAL;
if (errmsg != NULL)
strncpy(errmsg, "Invalid fspath", errmsg_len);