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kern linker: do not allow more than one kldload and kldunload syscalls simultaneously

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kld_sx is dropped e.g. for executing sysinits, which allows user
to initiate kldunload while module is not yet fully initialized.

Reviewed by:	markj
Differential revision:	https://reviews.freebsd.org/D30456
Sponsored by:	The FreeBSD Foundation
MFC after:	1 week
This commit is contained in:
Konstantin Belousov 2021-05-20 17:50:43 +03:00
parent 7c4342890b
commit e266a0f7f0
2 changed files with 77 additions and 18 deletions
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86
sys/kern/kern_linker.c
View File

@ -106,6 +106,7 @@ MALLOC_DEFINE(M_LINKER, "linker", "kernel linker");
linker_file_t linker_kernel_file;
static struct sx kld_sx; /* kernel linker lock */
static bool kld_busy;
/*
* Load counter used by clients to determine if a linker file has been
@ -1050,6 +1051,49 @@ linker_search_symbol_name(caddr_t value, char *buf, u_int buflen,
M_WAITOK));
}
int
linker_kldload_busy(int flags)
{
int error;
MPASS((flags & ~(LINKER_UB_UNLOCK | LINKER_UB_LOCKED |
LINKER_UB_PCATCH)) == 0);
if ((flags & LINKER_UB_LOCKED) != 0)
sx_assert(&kld_sx, SA_XLOCKED);
if ((flags & LINKER_UB_LOCKED) == 0)
sx_xlock(&kld_sx);
while (kld_busy) {
error = sx_sleep(&kld_busy, &kld_sx,
(flags & LINKER_UB_PCATCH) != 0 ? PCATCH : 0,
"kldbusy", 0);
if (error != 0) {
if ((flags & LINKER_UB_UNLOCK) != 0)
sx_xunlock(&kld_sx);
return (error);
}
}
kld_busy = true;
if ((flags & LINKER_UB_UNLOCK) != 0)
sx_xunlock(&kld_sx);
return (0);
}
void
linker_kldload_unbusy(int flags)
{
MPASS((flags & ~LINKER_UB_LOCKED) == 0);
if ((flags & LINKER_UB_LOCKED) != 0)
sx_assert(&kld_sx, SA_XLOCKED);
if ((flags & LINKER_UB_LOCKED) == 0)
sx_xlock(&kld_sx);
MPASS(kld_busy);
kld_busy = false;
wakeup(&kld_busy);
sx_xunlock(&kld_sx);
}
/*
* Syscalls.
*/
@ -1066,12 +1110,6 @@ kern_kldload(struct thread *td, const char *file, int *fileid)
if ((error = priv_check(td, PRIV_KLD_LOAD)) != 0)
return (error);
/*
* It is possible that kldloaded module will attach a new ifnet,
* so vnet context must be set when this ocurs.
*/
CURVNET_SET(TD_TO_VNET(td));
/*
* If file does not contain a qualified name or any dot in it
* (kldname.ko, or kldname.ver.ko) treat it as an interface
@ -1085,19 +1123,27 @@ kern_kldload(struct thread *td, const char *file, int *fileid)
modname = file;
}
sx_xlock(&kld_sx);
error = linker_load_module(kldname, modname, NULL, NULL, &lf);
if (error) {
error = linker_kldload_busy(LINKER_UB_PCATCH);
if (error != 0) {
sx_xunlock(&kld_sx);
goto done;
return (error);
}
lf->userrefs++;
if (fileid != NULL)
*fileid = lf->id;
sx_xunlock(&kld_sx);
done:
/*
* It is possible that kldloaded module will attach a new ifnet,
* so vnet context must be set when this ocurs.
*/
CURVNET_SET(TD_TO_VNET(td));
error = linker_load_module(kldname, modname, NULL, NULL, &lf);
CURVNET_RESTORE();
if (error == 0) {
lf->userrefs++;
if (fileid != NULL)
*fileid = lf->id;
}
linker_kldload_unbusy(LINKER_UB_LOCKED);
return (error);
}
@ -1132,8 +1178,13 @@ kern_kldunload(struct thread *td, int fileid, int flags)
if ((error = priv_check(td, PRIV_KLD_UNLOAD)) != 0)
return (error);
error = linker_kldload_busy(LINKER_UB_PCATCH);
if (error != 0) {
sx_xunlock(&kld_sx);
return (error);
}
CURVNET_SET(TD_TO_VNET(td));
sx_xlock(&kld_sx);
lf = linker_find_file_by_id(fileid);
if (lf) {
KLD_DPF(FILE, ("kldunload: lf->userrefs=%d\n", lf->userrefs));
@ -1153,9 +1204,8 @@ kern_kldunload(struct thread *td, int fileid, int flags)
}
} else
error = ENOENT;
sx_xunlock(&kld_sx);
CURVNET_RESTORE();
linker_kldload_unbusy(LINKER_UB_LOCKED);
return (error);
}

9
sys/sys/linker.h
View File

@ -196,6 +196,15 @@ int linker_search_symbol_name(caddr_t value, char *buf, u_int buflen,
/* HWPMC helper */
void *linker_hwpmc_list_objects(void);
/* kldload/kldunload syscalls blocking */
#define LINKER_UB_UNLOCK 0x0001 /* busy: unlock kld_sx locked on
return */
#define LINKER_UB_LOCKED 0x0002 /* busy/unbusy: kld_sx locked on
entry */
#define LINKER_UB_PCATCH 0x0004 /* busy: sleep interruptible */
int linker_kldload_busy(int flags);
void linker_kldload_unbusy(int flags);
#endif /* _KERNEL */
/*