Messages in this thread | | | From | "Rafael J. Wysocki" <> | Subject | Re: v2.6.28-rc1: readlink /proc/*/exe returns uninitialized data to userspace | Date | Sat, 25 Oct 2008 22:41:52 +0200 |
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On Saturday, 25 of October 2008, Vegard Nossum wrote: > Hi, > > When I run readlink on the /proc/*/exe-file for udevd, the kernel > returns some unitialized data to userspace: > > # strace -e trace=readlink readlink /proc/4762/exe > readlink("/proc/4762/exe", "/sbin/udevd", 1025) = 30 > > You can see it because the kernel thinks that the string is 30 bytes > long, but in fact it is only 12 (including the '\0'). > > If we explicitly clear the buffer before calling readlink, we can also > see that some garbage has been filled in there, after the string: > > # ./readlink /proc/4762/exe > readlink(/proc/4762/exe) = 30 > 2f7362696e2f7564657664000000ffffffad4effffffadffffffdeffffffffffffffff202864656c657465642900000000000000000000000000000 > > (Output is from following simple program:) > > #include <stdio.h> > #include <string.h> > #include <unistd.h> > > int main(int argc, char *argv[]) > { > char buf[1024]; > int i; > ssize_t n; > > memset(buf, 0, sizeof(buf)); > n = readlink(argv[1], buf, sizeof(buf)); > > printf("readlink(%s) = %d\n", argv[1], n); > > for (i = 0; i < sizeof(buf); ++i) > printf("%02x", buf[i]); > printf("\n"); > > return 0; > } > > It was discovered by kmemcheck: > > WARNING: kmemcheck: Caught 32-bit read from uninitialized memory (f6a109e4) > 64000000ad4eaddeffffffffffffffff000000000200000000000000c0838ff8 > i i u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u > ^ > > Pid: 21511, comm: readlink Not tainted (2.6.28-rc1 #58) 945P-A > EIP: 0060:[<c04f988d>] EFLAGS: 00000296 CPU: 0 > EIP is at __d_path+0x8d/0x1c0 > EAX: 0000000e EBX: d7ba0fe7 ECX: 00000001 EDX: f68b0b40 > ESI: f6a109e4 EDI: d7ba0fef EBP: e58c3f28 ESP: c2569c08 > DS: 007b ES: 007b FS: 00d8 GS: 0033 SS: 0068 > CR0: 8005003b CR2: f6c1d704 CR3: 31fc7000 CR4: 00000650 > DR0: 00000000 DR1: 00000000 DR2: 00000000 DR3: 00000000 > DR6: ffff4ff0 DR7: 00000400 > [<c04fa4b0>] d_path+0xb0/0xd0 > [<c052c37c>] proc_pid_readlink+0x6c/0xc0 > [<c04eda34>] sys_readlinkat+0x94/0xa0 > [<c04eda67>] sys_readlink+0x27/0x30 > [<c0422f83>] sysenter_do_call+0x12/0x3f > [<ffffffff>] 0xffffffff > > Line numbers are these (as of commit > e013e13bf605b9e6b702adffbe2853cfc60e7806 in Linus's tree): > > $ addr2line -e vmlinux -i c04f988d c04fa4b0 c052c37c c04eda34 c04eda67 > fs/dcache.c:1895 > fs/dcache.c:1901 > fs/dcache.c:1957 > fs/dcache.c:2016 > fs/proc/base.c:1347 > fs/proc/base.c:1374 > fs/stat.c:312 > fs/stat.c:325 > > I couldn't immediately figure out who/what to blame, please Cc in > right direction if you think you know it :-)
Well, I only can say who may be interested (CCs added).
Thanks, Rafael
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