Messages in this thread | | | Date | Mon, 13 Jun 2022 15:52:38 -0500 | Subject | Re: [PATCH v3] cred: Propagate security_prepare_creds() error code | From | Frederick Lawler <> |
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Hi Eric,
On 6/13/22 12:04 PM, Eric W. Biederman wrote: > Frederick Lawler <fred@cloudflare.com> writes: > >> While experimenting with the security_prepare_creds() LSM hook, we >> noticed that our EPERM error code was not propagated up the callstack. >> Instead ENOMEM is always returned. As a result, some tools may send a >> confusing error message to the user: >> >> $ unshare -rU >> unshare: unshare failed: Cannot allocate memory >> >> A user would think that the system didn't have enough memory, when >> instead the action was denied. >> >> This problem occurs because prepare_creds() and prepare_kernel_cred() >> return NULL when security_prepare_creds() returns an error code. Later, >> functions calling prepare_creds() and prepare_kernel_cred() return >> ENOMEM because they assume that a NULL meant there was no memory >> allocated. >> >> Fix this by propagating an error code from security_prepare_creds() up >> the callstack. > > Why would it make sense for security_prepare_creds to return an error > code other than ENOMEM? > > That seems a bit of a violation of what that function is supposed to do >
The API allows LSM authors to decide what error code is returned from the cred_prepare hook. security_task_alloc() is a similar hook, and has its return code propagated.
I'm proposing we follow security_task_allocs() pattern, and add visibility for failure cases in prepare_creds().
> I have probably missed a very interesting discussion where that was > mentioned but I don't see link to the discussion or anything explaining > why we want to do that in this change. >
AFAIK, this is the start of the discussion.
> Eric >
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