Messages in this thread | | | Date | Mon, 15 Mar 2021 13:29:02 +0300 | From | Dan Carpenter <> | Subject | Re: [PATCH] prctl: fix PR_SET_MM_AUXV kernel stack leak |
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On Sun, Mar 14, 2021 at 11:51:14PM +0300, Alexey Dobriyan wrote: > prctl(PR_SET_MM, PR_SET_MM_AUXV, addr, 1); > > will copy 1 byte from userspace to (quite big) on-stack array > and then stash everything to mm->saved_auxv.
What? It won't save everything, only the 1 byte. What am I not seeing?
kernel/sys.c 2073 static int prctl_set_auxv(struct mm_struct *mm, unsigned long addr, 2074 unsigned long len) 2075 { 2076 /* 2077 * This doesn't move the auxiliary vector itself since it's pinned to 2078 * mm_struct, but it permits filling the vector with new values. It's 2079 * up to the caller to provide sane values here, otherwise userspace 2080 * tools which use this vector might be unhappy. 2081 */ 2082 unsigned long user_auxv[AT_VECTOR_SIZE] = {}; 2083 2084 if (len > sizeof(user_auxv)) 2085 return -EINVAL; 2086 2087 if (copy_from_user(user_auxv, (const void __user *)addr, len)) ^^^^^^^^^ ^^^ Copies one byte from user space.
2088 return -EFAULT; 2089 2090 /* Make sure the last entry is always AT_NULL */ 2091 user_auxv[AT_VECTOR_SIZE - 2] = 0; 2092 user_auxv[AT_VECTOR_SIZE - 1] = 0; 2093 2094 BUILD_BUG_ON(sizeof(user_auxv) != sizeof(mm->saved_auxv)); 2095 2096 task_lock(current); 2097 memcpy(mm->saved_auxv, user_auxv, len); ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Saves one byte to mm->saved_auxv.
2098 task_unlock(current); 2099 2100 return 0; 2101 }
regards, dan carpenter
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