Messages in this thread Patch in this message | | | Date | Fri, 12 Sep 2008 22:36:24 +0200 | Subject | [RFC][PATCH] utsname: completely overwrite prior information | From | Vegard Nossum <> |
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From 25c69de4760e20cf7562cf92a55b65a71546093e Mon Sep 17 00:00:00 2001 From: Vegard Nossum <vegard.nossum@gmail.com> Date: Thu, 11 Sep 2008 19:59:50 +0200 Subject: [PATCH] utsname: completely overwrite prior information
On sethostname() and setdomainname(), previous information may be retained if it was longer than than the new hostname/domainname.
This can be demonstrated trivially by calling sethostname() first with a long name, then with a short name, and then calling uname() to retrieve the full buffer that contains the hostname (and possibly parts of the old hostname), one just has to look past the terminating zero.
I don't know if we should really care that much (hence the RFC); the only scenarios I can possibly think of is administrator putting something sensitive in the hostname (or domain name) by accident, and changing it back will not undo the mistake entirely, though it's not like we can recover gracefully from "rm -rf /" either... The other scenario is namespaces (CLONE_NEWUTS) where some information may be unintentionally "inherited" from the previous namespace (a program wants to hide the original name and does clone + sethostname, but some information is still left).
I think the patch may be defended on grounds of the principle of least surprise. But I am not adamant :-)
(I guess the question now is whether userspace should be able to write embedded NULs into the buffer or not...)
At least the observation has been made and the patch has been presented.
Signed-off-by: Vegard Nossum <vegard.nossum@gmail.com> --- kernel/sys.c | 6 ++++-- 1 files changed, 4 insertions(+), 2 deletions(-)
diff --git a/kernel/sys.c b/kernel/sys.c index 038a7bc..78b4515 100644 --- a/kernel/sys.c +++ b/kernel/sys.c @@ -1352,7 +1352,8 @@ asmlinkage long sys_sethostname(char __user *name, int len) errno = -EFAULT; if (!copy_from_user(tmp, name, len)) { memcpy(utsname()->nodename, tmp, len); - utsname()->nodename[len] = 0; + memset(utsname()->nodename + len, 0, + sizeof(utsname()->nodename) - len); errno = 0; } up_write(&uts_sem); @@ -1398,7 +1399,8 @@ asmlinkage long sys_setdomainname(char __user *name, int len) errno = -EFAULT; if (!copy_from_user(tmp, name, len)) { memcpy(utsname()->domainname, tmp, len); - utsname()->domainname[len] = 0; + memset(utsname()->domainname + len, 0, + sizeof(utsname()->domainname) - len); errno = 0; } up_write(&uts_sem); -- 1.5.5.1
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