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exec: Convert security_bprm_set_creds into security_bprm_repopulate_creds

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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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9
security/commoncap.c
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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),