exec: Convert security_bprm_set_creds into security_bprm_repopulate_creds

Rename bprm->cap_elevated to bprm->active_secureexec and initialize it
in prepare_binprm instead of in cap_bprm_set_creds.  Initializing
bprm->active_secureexec in prepare_binprm allows multiple
implementations of security_bprm_repopulate_creds to play nicely with
each other.

Rename security_bprm_set_creds to security_bprm_reopulate_creds to
emphasize that this path recomputes part of bprm->cred.  This
recomputation avoids the time of check vs time of use problems that
are inherent in unix #! interpreters.

In short two renames and a move in the location of initializing
bprm->active_secureexec.

Link: https://lkml.kernel.org/r/87o8qkzrxp.fsf_-_@x220.int.ebiederm.org
Acked-by: Linus Torvalds <torvalds@linux-foundation.org>
Reviewed-by: Kees Cook <keescook@chromium.org>
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
This commit is contained in:
Eric W. Biederman 2020-05-14 12:53:44 -05:00
parent b8bff59926
commit 112b714759
7 changed files with 19 additions and 20 deletions

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@ -1366,7 +1366,7 @@ int begin_new_exec(struct linux_binprm * bprm)
* the final state of setuid/setgid/fscaps can be merged into the
* secureexec flag.
*/
bprm->secureexec |= bprm->cap_elevated;
bprm->secureexec |= bprm->active_secureexec;
if (bprm->secureexec) {
/* Make sure parent cannot signal privileged process. */
@ -1634,10 +1634,10 @@ int prepare_binprm(struct linux_binprm *bprm)
int retval;
loff_t pos = 0;
/* Recompute parts of bprm->cred based on bprm->file */
bprm->active_secureexec = 0;
bprm_fill_uid(bprm);
/* fill in binprm security blob */
retval = security_bprm_set_creds(bprm);
retval = security_bprm_repopulate_creds(bprm);
if (retval)
return retval;

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@ -27,10 +27,10 @@ struct linux_binprm {
unsigned long argmin; /* rlimit marker for copy_strings() */
unsigned int
/*
* True if most recent call to cap_bprm_set_creds
* True if most recent call to security_bprm_set_creds
* resulted in elevated privileges.
*/
cap_elevated:1,
active_secureexec:1,
/*
* Set by bprm_creds_for_exec hook to indicate a
* privilege-gaining exec has happened. Used to set

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@ -50,7 +50,7 @@ LSM_HOOK(int, 0, settime, const struct timespec64 *ts,
const struct timezone *tz)
LSM_HOOK(int, 0, vm_enough_memory, struct mm_struct *mm, long pages)
LSM_HOOK(int, 0, bprm_creds_for_exec, struct linux_binprm *bprm)
LSM_HOOK(int, 0, bprm_set_creds, struct linux_binprm *bprm)
LSM_HOOK(int, 0, bprm_repopulate_creds, struct linux_binprm *bprm)
LSM_HOOK(int, 0, bprm_check_security, struct linux_binprm *bprm)
LSM_HOOK(void, LSM_RET_VOID, bprm_committing_creds, struct linux_binprm *bprm)
LSM_HOOK(void, LSM_RET_VOID, bprm_committed_creds, struct linux_binprm *bprm)

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@ -44,7 +44,7 @@
* request libc enable secure mode.
* @bprm contains the linux_binprm structure.
* Return 0 if the hook is successful and permission is granted.
* @bprm_set_creds:
* @bprm_repopulate_creds:
* Assuming that the relevant bits of @bprm->cred->security have been
* previously set, examine @bprm->file and regenerate them. This is
* so that the credentials derived from the interpreter the code is
@ -53,7 +53,7 @@
* reopen script, and may end up opening something completely different.
* This hook may also optionally check permissions (e.g. for
* transitions between security domains).
* The hook must set @bprm->cap_elevated to 1 if AT_SECURE should be set to
* The hook must set @bprm->active_secureexec to 1 if AT_SECURE should be set to
* request libc enable secure mode.
* @bprm contains the linux_binprm structure.
* Return 0 if the hook is successful and permission is granted.

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@ -140,7 +140,7 @@ extern int cap_capset(struct cred *new, const struct cred *old,
const kernel_cap_t *effective,
const kernel_cap_t *inheritable,
const kernel_cap_t *permitted);
extern int cap_bprm_set_creds(struct linux_binprm *bprm);
extern int cap_bprm_repopulate_creds(struct linux_binprm *bprm);
extern int cap_inode_setxattr(struct dentry *dentry, const char *name,
const void *value, size_t size, int flags);
extern int cap_inode_removexattr(struct dentry *dentry, const char *name);
@ -277,7 +277,7 @@ int security_syslog(int type);
int security_settime64(const struct timespec64 *ts, const struct timezone *tz);
int security_vm_enough_memory_mm(struct mm_struct *mm, long pages);
int security_bprm_creds_for_exec(struct linux_binprm *bprm);
int security_bprm_set_creds(struct linux_binprm *bprm);
int security_bprm_repopulate_creds(struct linux_binprm *bprm);
int security_bprm_check(struct linux_binprm *bprm);
void security_bprm_committing_creds(struct linux_binprm *bprm);
void security_bprm_committed_creds(struct linux_binprm *bprm);
@ -575,9 +575,9 @@ static inline int security_bprm_creds_for_exec(struct linux_binprm *bprm)
return 0;
}
static inline int security_bprm_set_creds(struct linux_binprm *bprm)
static inline int security_bprm_repopulate_creds(struct linux_binprm *bprm)
{
return cap_bprm_set_creds(bprm);
return cap_bprm_repopulate_creds(bprm);
}
static inline int security_bprm_check(struct linux_binprm *bprm)

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@ -797,14 +797,14 @@ static inline bool nonroot_raised_pE(struct cred *new, const struct cred *old,
}
/**
* cap_bprm_set_creds - Set up the proposed credentials for execve().
* cap_bprm_repopulate_creds - Set up the proposed credentials for execve().
* @bprm: The execution parameters, including the proposed creds
*
* Set up the proposed credentials for a new execution context being
* constructed by execve(). The proposed creds in @bprm->cred is altered,
* which won't take effect immediately. Returns 0 if successful, -ve on error.
*/
int cap_bprm_set_creds(struct linux_binprm *bprm)
int cap_bprm_repopulate_creds(struct linux_binprm *bprm)
{
const struct cred *old = current_cred();
struct cred *new = bprm->cred;
@ -884,12 +884,11 @@ int cap_bprm_set_creds(struct linux_binprm *bprm)
return -EPERM;
/* Check for privilege-elevated exec. */
bprm->cap_elevated = 0;
if (is_setid ||
(!__is_real(root_uid, new) &&
(effective ||
__cap_grew(permitted, ambient, new))))
bprm->cap_elevated = 1;
bprm->active_secureexec = 1;
return 0;
}
@ -1346,7 +1345,7 @@ static struct security_hook_list capability_hooks[] __lsm_ro_after_init = {
LSM_HOOK_INIT(ptrace_traceme, cap_ptrace_traceme),
LSM_HOOK_INIT(capget, cap_capget),
LSM_HOOK_INIT(capset, cap_capset),
LSM_HOOK_INIT(bprm_set_creds, cap_bprm_set_creds),
LSM_HOOK_INIT(bprm_repopulate_creds, cap_bprm_repopulate_creds),
LSM_HOOK_INIT(inode_need_killpriv, cap_inode_need_killpriv),
LSM_HOOK_INIT(inode_killpriv, cap_inode_killpriv),
LSM_HOOK_INIT(inode_getsecurity, cap_inode_getsecurity),

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@ -828,9 +828,9 @@ int security_bprm_creds_for_exec(struct linux_binprm *bprm)
return call_int_hook(bprm_creds_for_exec, 0, bprm);
}
int security_bprm_set_creds(struct linux_binprm *bprm)
int security_bprm_repopulate_creds(struct linux_binprm *bprm)
{
return call_int_hook(bprm_set_creds, 0, bprm);
return call_int_hook(bprm_repopulate_creds, 0, bprm);
}
int security_bprm_check(struct linux_binprm *bprm)