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kcov: move thread attach from open to start

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The current kcov code attaches a kcov object to the thread which opened
it. This is not desirable, as syzkaller opens /dev/kcov in a parent
process and passes it down to the child.

Move the thread attachment from open() time to start time.
This commit is contained in:
Matheus
2026-10-08 14:41:34 -03:00
parent d999ab7de2
commit 9a9740469f
4 changed files with 46 additions and 53 deletions
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kernel-src/sys/kcov_dev.c
+8 -28
View File
@@ -89,10 +89,6 @@ static int create_node_for_kcov(kcov_t *kcov, int minor, vnode_t **vnodep) {
kcov->vnode_handle = vnode;
devfs_remove_anonymous(DEV_MAJOR_KCOV, minor);
// a kcov will have two references initially:
// - one for the thread holding it
// - one for the vnode
kcov_hold(kcov);
*vnodep = vnode;
return 0;
}
@@ -103,18 +99,6 @@ static int open(int oldminor, vnode_t **vnodep, int flags) {
if (oldminor != KCOV_MAX)
return ENODEV;
// if the thread already has a kcov attached, return it
if (current_thread()->kcov) {
kcov_t *kcov = current_thread()->kcov;
int error = create_node_for_kcov(kcov, kcov->minor, vnodep);
if (error)
return error;
VOP_RELEASE(old);
return 0;
}
int minor;
int error = allocate_kcov(&minor);
if (error)
@@ -127,7 +111,6 @@ static int open(int oldminor, vnode_t **vnodep, int flags) {
return error;
}
current_thread()->kcov = kcov;
VOP_RELEASE(old);
return 0;
}
@@ -137,8 +120,8 @@ static int open(int oldminor, vnode_t **vnodep, int flags) {
#define IOCTL_REQUEST_SET_SIZE 0xF1177200
static int ioctl(int minor, unsigned long request, void *arg, int *result, cred_t *cred) {
kcov_t *kcov = current_thread()->kcov;
if (kcov == NULL || kcov->minor != minor)
kcov_t *kcov = get_kcov(minor);
if (kcov == NULL)
return EINVAL;
switch (request) {
@@ -148,24 +131,21 @@ static int ioctl(int minor, unsigned long request, void *arg, int *result, cred_
if (error)
return error;
return kcov_set_buffer_size(size);
return kcov_set_buffer_size(kcov, size);
}
case IOCTL_REQUEST_START: {
if (kcov->mode != KCOV_MODE_DISABLED)
return EBUSY;
if (kcov->buffer == NULL)
return EINVAL;
int mode;
int error = USERCOPY_POSSIBLY_FROM_USER(&mode, arg, sizeof(mode));
if (error)
return error;
return kcov_set_mode(mode);
if (mode != KCOV_MODE_PC && mode != KCOV_MODE_CMP)
return EINVAL;
return kcov_set_mode(kcov, mode);
}
case IOCTL_REQUEST_STOP:
return kcov_set_mode(KCOV_MODE_DISABLED);
return kcov_set_mode(kcov, KCOV_MODE_DISABLED);
default:
return ENOTTY;
}