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    SubjectRe: [PATCH] proc: maps protection
    The /proc/pid/ "maps", "smaps", and "numa_maps" files contain sensitive 
    information about the memory location and usage of processes. Issues:

    - maps should not be world-readable, especially if programs expect any
    kind of ASLR protection from local attackers.
    - maps cannot just be 0400 because "-D_FORTIFY_SOURCE=2 -O2" makes glibc
    check the maps when %n is in a *printf call, and a setuid(getuid())
    process wouldn't be able to read its own maps file. (For reference
    see http://lkml.org/lkml/2006/1/22/150)
    - a system-wide toggle is needed to allow prior behavior in the case of
    non-root applications that depend on access to the maps contents.

    This change implements a check using "ptrace_may_attach" before allowing
    access to read the maps contents. To control this protection, the new
    knob /proc/sys/kernel/maps_protect has been added, with corresponding
    updates to the procfs documentation.

    Signed-off-by: Kees Cook <kees@outflux.net>
    ---
    CREDITS | 2 +-
    Documentation/filesystems/proc.txt | 7 +++++++
    fs/proc/base.c | 3 +++
    fs/proc/internal.h | 2 ++
    fs/proc/task_mmu.c | 16 +++++++++++++++-
    fs/proc/task_nommu.c | 6 ++++++
    include/linux/sysctl.h | 1 +
    kernel/sysctl.c | 9 +++++++++
    8 files changed, 44 insertions(+), 2 deletions(-)
    ---
    diff --git a/CREDITS b/CREDITS
    index 6bd8ab8..38c3ada 100644
    --- a/CREDITS
    +++ b/CREDITS
    @@ -655,7 +655,7 @@ N: Kees Cook
    E: kees@outflux.net
    W: http://outflux.net/
    P: 1024D/17063E6D 9FA3 C49C 23C9 D1BC 2E30 1975 1FFF 4BA9 1706 3E6D
    -D: Minor updates to SCSI code for the Communications type
    +D: Minor updates to SCSI types, added /proc/pid/maps protection
    S: (ask for current address)
    S: USA

    diff --git a/Documentation/filesystems/proc.txt b/Documentation/filesystems/proc.txt
    index 5484ab5..d9b06b5 100644
    --- a/Documentation/filesystems/proc.txt
    +++ b/Documentation/filesystems/proc.txt
    @@ -1137,6 +1137,13 @@ determine whether or not they are still functioning properly.
    Because the NMI watchdog shares registers with oprofile, by disabling the NMI
    watchdog, oprofile may have more registers to utilize.

    +maps_protect
    +------------
    +
    +Enables/Disables the protection of the per-process proc entries "maps" and
    +"smaps". When enabled, the contents of these files are visible only to
    +readers that are allowed to ptrace() the given process.
    +

    2.4 /proc/sys/vm - The virtual memory subsystem
    -----------------------------------------------
    diff --git a/fs/proc/base.c b/fs/proc/base.c
    index 01f7769..6feccbc 100644
    --- a/fs/proc/base.c
    +++ b/fs/proc/base.c
    @@ -123,6 +123,9 @@ struct pid_entry {
    NULL, &proc_info_file_operations, \
    { .proc_read = &proc_##OTYPE } )

    +int maps_protect = 0;
    +EXPORT_SYMBOL(maps_protect);
    +
    static struct fs_struct *get_fs_struct(struct task_struct *task)
    {
    struct fs_struct *fs;
    diff --git a/fs/proc/internal.h b/fs/proc/internal.h
    index c932aa6..2c65b6e 100644
    --- a/fs/proc/internal.h
    +++ b/fs/proc/internal.h
    @@ -33,6 +33,8 @@ do { \
    extern int nommu_vma_show(struct seq_file *, struct vm_area_struct *);
    #endif

    +extern int maps_protect;
    +
    extern void create_seq_entry(char *name, mode_t mode, const struct file_operations *f);
    extern int proc_exe_link(struct inode *, struct dentry **, struct vfsmount **);
    extern int proc_tid_stat(struct task_struct *, char *);
    diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
    index 7445980..45a0f3e 100644
    --- a/fs/proc/task_mmu.c
    +++ b/fs/proc/task_mmu.c
    @@ -134,6 +134,9 @@ static int show_map_internal(struct seq_file *m, void *v, struct mem_size_stats
    dev_t dev = 0;
    int len;

    + if (maps_protect && !ptrace_may_attach(task))
    + return -EACCES;
    +
    if (file) {
    struct inode *inode = vma->vm_file->f_path.dentry->d_inode;
    dev = inode->i_sb->s_dev;
    @@ -444,11 +447,22 @@ const struct file_operations proc_maps_operations = {
    #ifdef CONFIG_NUMA
    extern int show_numa_map(struct seq_file *m, void *v);

    +static int show_numa_map_checked(struct seq_file *m, void *v)
    +{
    + struct proc_maps_private *priv = m->private;
    + struct task_struct *task = priv->task;
    +
    + if (maps_protect && !ptrace_may_attach(task))
    + return -EACCES;
    +
    + return show_numa_map(m, v);
    +}
    +
    static struct seq_operations proc_pid_numa_maps_op = {
    .start = m_start,
    .next = m_next,
    .stop = m_stop,
    - .show = show_numa_map
    + .show = show_numa_map_checked
    };

    static int numa_maps_open(struct inode *inode, struct file *file)
    diff --git a/fs/proc/task_nommu.c b/fs/proc/task_nommu.c
    index 7cddf6b..c2747c9 100644
    --- a/fs/proc/task_nommu.c
    +++ b/fs/proc/task_nommu.c
    @@ -143,6 +143,12 @@ out:
    static int show_map(struct seq_file *m, void *_vml)
    {
    struct vm_list_struct *vml = _vml;
    + struct proc_maps_private *priv = m->private;
    + struct task_struct *task = priv->task;
    +
    + if (maps_protect && !ptrace_may_attach(task))
    + return -EACCES;
    +
    return nommu_vma_show(m, vml->vma);
    }

    diff --git a/include/linux/sysctl.h b/include/linux/sysctl.h
    index 2c5fb38..608a331 100644
    --- a/include/linux/sysctl.h
    +++ b/include/linux/sysctl.h
    @@ -165,6 +165,7 @@ enum
    KERN_MAX_LOCK_DEPTH=74,
    KERN_NMI_WATCHDOG=75, /* int: enable/disable nmi watchdog */
    KERN_PANIC_ON_NMI=76, /* int: whether we will panic on an unrecovered */
    + KERN_MAPS_PROTECT=77, /* int: whether we protect maps from public visibility */
    };


    diff --git a/kernel/sysctl.c b/kernel/sysctl.c
    index 1b255df..ca4d69f 100644
    --- a/kernel/sysctl.c
    +++ b/kernel/sysctl.c
    @@ -76,6 +76,7 @@ extern int pid_max_min, pid_max_max;
    extern int sysctl_drop_caches;
    extern int percpu_pagelist_fraction;
    extern int compat_log;
    +extern int maps_protect;

    /* this is needed for the proc_dointvec_minmax for [fs_]overflow UID and GID */
    static int maxolduid = 65535;
    @@ -603,6 +604,14 @@ static ctl_table kern_table[] = {
    .proc_handler = &proc_dointvec,
    },
    #endif
    + {,
    + .ctl_name = KERN_MAPS_PROTECT,
    + .procname = "maps_protect",
    + .data = &maps_protect,
    + .maxlen = sizeof(int),
    + .mode = 0644,
    + .proc_handler = &proc_dointvec,
    + },

    { .ctl_name = 0 }
    };


    --
    Kees Cook
    -
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