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Date: Tue, 13 Mar 2012 11:18:12 +0400 From: Cyrill Gorcunov <gorcunov@...nvz.org> To: Matt Helsley <matthltc@...ibm.com>, Oleg Nesterov <oleg@...hat.com> Cc: KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>, Pavel Emelyanov <xemul@...allels.com>, Kees Cook <keescook@...omium.org>, Tejun Heo <tj@...nel.org>, Andrew Morton <akpm@...ux-foundation.org>, LKML <linux-kernel@...r.kernel.org> Subject: Re: [RFC] c/r: prctl: Add ability to set new mm_struct::exe_file v3 On Tue, Mar 13, 2012 at 10:26:25AM +0400, Cyrill Gorcunov wrote: > > I am quite aware of the c/r use for this prctl :). However I also > > wonder if there aren't serious malicious uses of it. I'm not saying the > > symlink has to be perfectly accurate at all times, but it's easy and > > reasonable to make it much harder to abuse this particular prctl for > > malicious purposes by making it one-shot. > > > > ok, convinced, I'll update the patch ;) Matt, Oleg, there is a final version I hope, which should fit everyone. Cyrill --- From: Cyrill Gorcunov <gorcunov@...nvz.org> Subject: c/r: prctl: Add ability to set new mm_struct::exe_file When we do restore we would like to have a way to setup a former mm_struct::exe_file so that /proc/pid/exe would point to the original executable file a process had at checkpoint time. For this the PR_SET_MM_EXE_FILE code is introduced. This option takes a file descriptor which will be set as a source for new /proc/$pid/exe symlink. Note it allows to change /proc/$pid/exe iif there are no VM_EXECUTABLE vmas present for current process, simply because this feature is a special to C/R and mm::num_exe_file_vmas become meaningless after that. Also this action is one-shot only. For secutiry reason we don't allow to chanage the symlink several times. This feature is available iif CONFIG_CHECKPOINT_RESTORE is set. Signed-off-by: Cyrill Gorcunov <gorcunov@...nvz.org> Reviewed-by: Oleg Nesterov <oleg@...hat.com> CC: KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com> CC: Pavel Emelyanov <xemul@...allels.com> CC: Kees Cook <keescook@...omium.org> CC: Tejun Heo <tj@...nel.org> CC: Matt Helsley <matthltc@...ibm.com> --- include/linux/prctl.h | 1 kernel/sys.c | 59 ++++++++++++++++++++++++++++++++++++++++++++++++++ 2 files changed, 60 insertions(+) Index: linux-2.6.git/include/linux/prctl.h =================================================================== --- linux-2.6.git.orig/include/linux/prctl.h +++ linux-2.6.git/include/linux/prctl.h @@ -118,5 +118,6 @@ # define PR_SET_MM_ENV_START 10 # define PR_SET_MM_ENV_END 11 # define PR_SET_MM_AUXV 12 +# define PR_SET_MM_EXE_FILE 13 #endif /* _LINUX_PRCTL_H */ Index: linux-2.6.git/kernel/sys.c =================================================================== --- linux-2.6.git.orig/kernel/sys.c +++ linux-2.6.git/kernel/sys.c @@ -36,6 +36,8 @@ #include <linux/personality.h> #include <linux/ptrace.h> #include <linux/fs_struct.h> +#include <linux/file.h> +#include <linux/mount.h> #include <linux/gfp.h> #include <linux/syscore_ops.h> #include <linux/version.h> @@ -1701,6 +1703,60 @@ static bool vma_flags_mismatch(struct vm (vma->vm_flags & banned); } +static int prctl_set_mm_exe_file(struct mm_struct *mm, unsigned int fd) +{ + struct file *exe_file; + struct dentry *dentry; + int err; + + /* + * Setting new mm::exe_file is only allowed + * when no VM_EXECUTABLE vma's left. This is + * a special C/R case when a restored program + * need to change own /proc/$pid/exe symlink. + * After this call mm::num_exe_file_vmas become + * meaningless. + */ + if (mm->num_exe_file_vmas) + return -EBUSY; + + exe_file = fget(fd); + if (!exe_file) + return -EBADF; + + dentry = exe_file->f_path.dentry; + + /* + * Because the original mm->exe_file + * points to executable file, make sure + * this one is executable as well to not + * break an overall picture. + */ + err = -EACCES; + if (!S_ISREG(dentry->d_inode->i_mode) || + exe_file->f_path.mnt->mnt_flags & MNT_NOEXEC) + goto exit; + + err = inode_permission(dentry->d_inode, MAY_EXEC); + if (err) + goto exit; + + /* + * For security reason changing mm->exe_file + * is one-shot action. + */ + down_write(&mm->mmap_sem); + if (likely(!mm->exe_file)) + set_mm_exe_file(mm, exe_file); + else + err = -EBUSY; + up_write(&mm->mmap_sem); + +exit: + fput(exe_file); + return err; +} + static int prctl_set_mm(int opt, unsigned long addr, unsigned long arg4, unsigned long arg5) { @@ -1715,6 +1771,9 @@ static int prctl_set_mm(int opt, unsigne if (!capable(CAP_SYS_RESOURCE)) return -EPERM; + if (opt == PR_SET_MM_EXE_FILE) + return prctl_set_mm_exe_file(mm, (unsigned int)addr); + if (addr >= TASK_SIZE) return -EINVAL; -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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