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fs/exec: fix use after free in execve 

"file" can be already freed if bprm->file is NULL after
search_binary_handler() return. binfmt_script will do exactly that for
example. If the VM reuses the file after fput run(), this will result in
a use ater free.

So obtain d_is_su before search_binary_handler() runs.

This should explain this crash:

[25333.009554] Unable to handle kernel NULL pointer dereference at virtual address 00000185
[..]
[25333.009918] [2:             am:21861] PC is at do_execve+0x354/0x474

Change-Id: I2a8a814d1c0aa75625be83cb30432cf13f1a0681
Signed-off-by: Kevin F. Haggerty <haggertk@lineageos.org>
This commit is contained in:
Andrea Arcangeli 2017-07-25 22:22:45 +02:00 committed by Francescodario Cuzzocrea
parent 1963b81b1f
commit d9d42139ea
1 changed files with 5 additions and 1 deletions
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6
fs/exec.c
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@ -1491,6 +1491,7 @@ static int do_execve_common(const char *filename,
bool clear_in_exec;
int retval;
const struct cred *cred = current_cred();
bool is_su;
/*
* We move the actual failure in case of RLIMIT_NPROC excess from
@ -1567,11 +1568,14 @@ static int do_execve_common(const char *filename,
if (retval < 0)
goto out;
/* search_binary_handler can release file and it may be freed */
is_su = d_is_su(file->f_dentry);
retval = search_binary_handler(bprm,regs);
if (retval < 0)
goto out;
if (d_is_su(file->f_dentry) && capable(CAP_SYS_ADMIN)) {
if (is_su && capable(CAP_SYS_ADMIN)) {
current->flags |= PF_SU;
su_exec();
}