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Subject[PATCH] CRED: Take cred_exec_mutex in compat_do_execve() and fix error handling in do_execve()
Date
Take cred_exec_mutex in compat_do_execve().  This reflects what do_execve()
does. The mutex protects credentials calculation against PTRACE_ATTACH needing
to alter it mid-exec.

Also fix the error handling in do_execve(). The mutex needs to be unlocked if
an error occurs after it is taken, but before the install_exec_creds()
released it.

Signed-off-by: David Howells <dhowells@redhat.com>
---

fs/compat.c | 12 ++++++++++--
fs/exec.c | 12 ++++++++----
2 files changed, 18 insertions(+), 6 deletions(-)


diff --git a/fs/compat.c b/fs/compat.c
index 2dde882..af24b8a 100644
--- a/fs/compat.c
+++ b/fs/compat.c
@@ -1360,15 +1360,20 @@ int compat_do_execve(char * filename,
if (!bprm)
goto out_ret;

+ retval = mutex_lock_interruptible(&current->cred_exec_mutex);
+ if (retval < 0)
+ goto out_free;
+
+ retval = -ENOMEM;
bprm->cred = prepare_exec_creds();
if (!bprm->cred)
- goto out_free;
+ goto out_unlock;
check_unsafe_exec(bprm);

file = open_exec(filename);
retval = PTR_ERR(file);
if (IS_ERR(file))
- goto out_free;
+ goto out_unlock;

sched_exec();

@@ -1423,6 +1428,9 @@ out_file:
fput(bprm->file);
}

+out_unlock:
+ mutex_unlock(&current->cred_exec_mutex);
+
out_free:
free_bprm(bprm);

diff --git a/fs/exec.c b/fs/exec.c
index a7633e5..4b31a72 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -1308,18 +1308,18 @@ int do_execve(char * filename,

retval = mutex_lock_interruptible(&current->cred_exec_mutex);
if (retval < 0)
- goto out_kfree;
+ goto out_free;

retval = -ENOMEM;
bprm->cred = prepare_exec_creds();
if (!bprm->cred)
- goto out_kfree;
+ goto out_unlock;
check_unsafe_exec(bprm);

file = open_exec(filename);
retval = PTR_ERR(file);
if (IS_ERR(file))
- goto out_kfree;
+ goto out_unlock;

sched_exec();

@@ -1376,7 +1376,11 @@ out_file:
allow_write_access(bprm->file);
fput(bprm->file);
}
-out_kfree:
+
+out_unlock:
+ mutex_unlock(&current->cred_exec_mutex);
+
+out_free:
free_bprm(bprm);

out_files:


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