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Commit 6405c695 authored by Nick Pelly's avatar Nick Pelly
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Clean fix for the chown race condition on new input devices. 

Drop init's egid to AID_INPUT while creating the device node, so that it is
created with the correct gid. This eliminates the
possibility of system_server opening the device node before its permissions
are set correctly.

Using setegid() allows us to swap back to AID_ROOT immediately after mknod().

Bug: 2375632
parent 25eab084

init/devices.c

+8 −1
Original line number Diff line number Diff line
@@ -306,8 +306,15 @@ static void make_device(const char *path, int block, int major, int minor) 


    mode = get_device_perm(path, &uid, &gid) | (block ? S_IFBLK : S_IFCHR);

    dev = (major << 8) | minor;

    /* Temporarily change egid to avoid race condition setting the gid of the

     * device node. Unforunately changing the euid would prevent creation of

     * some device nodes, so the uid has to be set with chown() and is still

     * racy. Fixing the gid race at least fixed the issue with system_server

     * opening dynamic input devices under the AID_INPUT gid. */

    setegid(gid);

    mknod(path, mode, dev);

    chown(path, uid, gid);

    chown(path, uid, -1);

    setegid(AID_ROOT);

}



#if LOG_UEVENTS