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    Subject[PATCH 6.0 165/862] tracing: Fix reading strings from synthetic events
    Date
    From: Steven Rostedt (Google) <rostedt@goodmis.org>

    commit 0934ae9977c27133449b6dd8c6213970e7eece38 upstream.

    The follow commands caused a crash:

    # cd /sys/kernel/tracing
    # echo 's:open char file[]' > dynamic_events
    # echo 'hist:keys=common_pid:file=filename:onchange($file).trace(open,$file)' > events/syscalls/sys_enter_openat/trigger'
    # echo 1 > events/synthetic/open/enable

    BOOM!

    The problem is that the synthetic event field "char file[]" will read
    the value given to it as a string without any memory checks to make sure
    the address is valid. The above example will pass in the user space
    address and the sythetic event code will happily call strlen() on it
    and then strscpy() where either one will cause an oops when accessing
    user space addresses.

    Use the helper functions from trace_kprobe and trace_eprobe that can
    read strings safely (and actually succeed when the address is from user
    space and the memory is mapped in).

    Now the above can show:

    packagekitd-1721 [000] ...2. 104.597170: open: file=/usr/lib/rpm/fileattrs/cmake.attr
    in:imjournal-978 [006] ...2. 104.599642: open: file=/var/lib/rsyslog/imjournal.state.tmp
    packagekitd-1721 [000] ...2. 104.626308: open: file=/usr/lib/rpm/fileattrs/debuginfo.attr

    Link: https://lkml.kernel.org/r/20221012104534.826549315@goodmis.org

    Cc: stable@vger.kernel.org
    Cc: Andrew Morton <akpm@linux-foundation.org>
    Cc: Tom Zanussi <zanussi@kernel.org>
    Acked-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
    Reviewed-by: Tom Zanussi <zanussi@kernel.org>
    Fixes: bd82631d7ccdc ("tracing: Add support for dynamic strings to synthetic events")
    Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    ---
    kernel/trace/trace_events_synth.c | 23 +++++++++++++++++------
    1 file changed, 17 insertions(+), 6 deletions(-)

    --- a/kernel/trace/trace_events_synth.c
    +++ b/kernel/trace/trace_events_synth.c
    @@ -17,6 +17,8 @@
    /* for gfp flag names */
    #include <linux/trace_events.h>
    #include <trace/events/mmflags.h>
    +#include "trace_probe.h"
    +#include "trace_probe_kernel.h"

    #include "trace_synth.h"

    @@ -409,6 +411,7 @@ static unsigned int trace_string(struct
    {
    unsigned int len = 0;
    char *str_field;
    + int ret;

    if (is_dynamic) {
    u32 data_offset;
    @@ -417,19 +420,27 @@ static unsigned int trace_string(struct
    data_offset += event->n_u64 * sizeof(u64);
    data_offset += data_size;

    - str_field = (char *)entry + data_offset;
    -
    - len = strlen(str_val) + 1;
    - strscpy(str_field, str_val, len);
    + len = kern_fetch_store_strlen((unsigned long)str_val);

    data_offset |= len << 16;
    *(u32 *)&entry->fields[*n_u64] = data_offset;

    + ret = kern_fetch_store_string((unsigned long)str_val, &entry->fields[*n_u64], entry);
    +
    (*n_u64)++;
    } else {
    str_field = (char *)&entry->fields[*n_u64];

    - strscpy(str_field, str_val, STR_VAR_LEN_MAX);
    +#ifdef CONFIG_ARCH_HAS_NON_OVERLAPPING_ADDRESS_SPACE
    + if ((unsigned long)str_val < TASK_SIZE)
    + ret = strncpy_from_user_nofault(str_field, str_val, STR_VAR_LEN_MAX);
    + else
    +#endif
    + ret = strncpy_from_kernel_nofault(str_field, str_val, STR_VAR_LEN_MAX);
    +
    + if (ret < 0)
    + strcpy(str_field, FAULT_STRING);
    +
    (*n_u64) += STR_VAR_LEN_MAX / sizeof(u64);
    }

    @@ -462,7 +473,7 @@ static notrace void trace_event_raw_even
    val_idx = var_ref_idx[field_pos];
    str_val = (char *)(long)var_ref_vals[val_idx];

    - len = strlen(str_val) + 1;
    + len = kern_fetch_store_strlen((unsigned long)str_val);

    fields_size += len;
    }

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