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mpv/player/screenshot.c
nanahi 9a861c930b image_writer: fix TOCTOU in screenshot filename generation 
The screenshot command is documented to not overwrite existing files.
However, there is a race window between the filename is generated with
gen_fname and when the file is open to write. Specifically, the
convert_image function in this window can be very time consuming
depending on video and screenshot image format and size. This results
in existing file being overwritten because the file writing functions
don't check for the existance of file.

Fix this be opening the file in exclusive mode. Add overwrite parameter to
write_image for other operations that are documented to overwrite existing
files, like screenshot-to-file. Note that for write_avif, checking
existance is used instead because avio_open does not support exclusive
open mode.
2024-03-19 19:30:27 +01:00

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/*
* This file is part of mpv.
*
* mpv is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public
* License as published by the Free Software Foundation; either
* version 2.1 of the License, or (at your option) any later version.
*
* mpv is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public
* License along with mpv. If not, see <http://www.gnu.org/licenses/>.
*/
#include <stdlib.h>
#include <string.h>
#include <time.h>
#include <libavcodec/avcodec.h>
#include "common/global.h"
#include "osdep/io.h"
#include "mpv_talloc.h"
#include "screenshot.h"
#include "core.h"
#include "command.h"
#include "input/cmd.h"
#include "misc/bstr.h"
#include "misc/dispatch.h"
#include "misc/node.h"
#include "misc/thread_tools.h"
#include "common/msg.h"
#include "options/path.h"
#include "video/mp_image.h"
#include "video/mp_image_pool.h"
#include "video/out/vo.h"
#include "video/image_writer.h"
#include "video/sws_utils.h"
#include "sub/osd.h"
#include "video/csputils.h"
#define MODE_FULL_WINDOW 1
#define MODE_SUBTITLES 2
typedef struct screenshot_ctx {
struct MPContext *mpctx;
struct mp_log *log;
// Command to repeat in each-frame mode.
struct mp_cmd *each_frame;
int frameno;
uint64_t last_frame_count;
} screenshot_ctx;
void screenshot_init(struct MPContext *mpctx)
{
mpctx->screenshot_ctx = talloc(mpctx, screenshot_ctx);
*mpctx->screenshot_ctx = (screenshot_ctx) {
.mpctx = mpctx,
.frameno = 1,
.log = mp_log_new(mpctx, mpctx->log, "screenshot")
};
}
static char *stripext(void *talloc_ctx, const char *s)
{
const char *end = strrchr(s, '.');
if (!end)
end = s + strlen(s);
return talloc_asprintf(talloc_ctx, "%.*s", (int)(end - s), s);
}
static bool write_screenshot(struct mp_cmd_ctx *cmd, struct mp_image *img,
const char *filename, struct image_writer_opts *opts,
bool overwrite)
{
struct MPContext *mpctx = cmd->mpctx;
struct image_writer_opts *gopts = mpctx->opts->screenshot_image_opts;
struct image_writer_opts opts_copy = opts ? *opts : *gopts;
mp_cmd_msg(cmd, MSGL_V, "Starting screenshot: '%s'", filename);
mp_core_unlock(mpctx);
bool ok = img && write_image(img, &opts_copy, filename, mpctx->global,
mpctx->screenshot_ctx->log, overwrite);
mp_core_lock(mpctx);
if (ok) {
mp_cmd_msg(cmd, MSGL_INFO, "Screenshot: '%s'", filename);
} else {
mp_cmd_msg(cmd, MSGL_ERR, "Error writing screenshot!");
}
return ok;
}
#ifdef _WIN32
#define ILLEGAL_FILENAME_CHARS "?\"/\\<>*|:"
#else
#define ILLEGAL_FILENAME_CHARS "/"
#endif
// Replace all characters disallowed in filenames with '_' and return the newly
// allocated result string.
static char *sanitize_filename(void *talloc_ctx, const char *s)
{
char *res = talloc_strdup(talloc_ctx, s);
char *cur = res;
while (*cur) {
if (strchr(ILLEGAL_FILENAME_CHARS, *cur) || ((unsigned char)*cur) < 32)
*cur = '_';
cur++;
}
return res;
}
static void append_filename(char **s, const char *f)
{
char *append = sanitize_filename(NULL, f);
*s = talloc_strdup_append(*s, append);
talloc_free(append);
}
static char *create_fname(struct MPContext *mpctx, char *template,
const char *file_ext, int *sequence, int *frameno)
{
char *res = talloc_strdup(NULL, ""); //empty string, non-NULL context
time_t raw_time = time(NULL);
struct tm *local_time = localtime(&raw_time);
if (!template || *template == '\0')
return NULL;
for (;;) {
char *next = strchr(template, '%');
if (!next)
break;
res = talloc_strndup_append(res, template, next - template);
template = next + 1;
char fmt = *template++;
switch (fmt) {
case '#':
case '0':
case 'n': {
int digits = '4';
if (fmt == '#') {
if (!*sequence) {
*frameno = 1;
}
fmt = *template++;
}
if (fmt == '0') {
digits = *template++;
if (digits < '0' || digits > '9')
goto error_exit;
fmt = *template++;
}
if (fmt != 'n')
goto error_exit;
char fmtstr[] = {'%', '0', digits, 'd', '\0'};
res = talloc_asprintf_append(res, fmtstr, *frameno);
if (*frameno < INT_MAX - 1) {
(*frameno) += 1;
(*sequence) += 1;
}
break;
}
case 'f':
case 'F': {
char *video_file = NULL;
if (mpctx->filename)
video_file = mp_basename(mpctx->filename);
if (!video_file)
video_file = "NO_FILE";
char *name = video_file;
if (fmt == 'F')
name = stripext(res, video_file);
append_filename(&res, name);
break;
}
case 'x':
case 'X': {
char *fallback = "";
if (fmt == 'X') {
if (template[0] != '{')
goto error_exit;
char *end = strchr(template, '}');
if (!end)
goto error_exit;
fallback = talloc_strndup(res, template + 1, end - template - 1);
template = end + 1;
}
if (!mpctx->filename || mp_is_url(bstr0(mpctx->filename))) {
res = talloc_strdup_append(res, fallback);
} else {
bstr dir = mp_dirname(mpctx->filename);
if (!bstr_equals0(dir, "."))
res = talloc_asprintf_append(res, "%.*s", BSTR_P(dir));
}
break;
}
case 'p':
case 'P': {
char *t = mp_format_time(get_playback_time(mpctx), fmt == 'P');
append_filename(&res, t);
talloc_free(t);
break;
}
case 'w': {
char tfmt = *template;
if (!tfmt)
goto error_exit;
template++;
char fmtstr[] = {'%', tfmt, '\0'};
char *s = mp_format_time_fmt(fmtstr, get_playback_time(mpctx));
if (!s)
goto error_exit;
append_filename(&res, s);
talloc_free(s);
break;
}
case 't': {
char tfmt = *template;
if (!tfmt)
goto error_exit;
template++;
char fmtstr[] = {'%', tfmt, '\0'};
char buffer[80];
if (strftime(buffer, sizeof(buffer), fmtstr, local_time) == 0)
buffer[0] = '\0';
append_filename(&res, buffer);
break;
}
case '{': {
char *end = strchr(template, '}');
if (!end)
goto error_exit;
struct bstr prop = bstr_splice(bstr0(template), 0, end - template);
char *tmp = talloc_asprintf(NULL, "${%.*s}", BSTR_P(prop));
char *s = mp_property_expand_string(mpctx, tmp);
talloc_free(tmp);
if (s)
append_filename(&res, s);
talloc_free(s);
template = end + 1;
break;
}
case '%':
res = talloc_strdup_append(res, "%");
break;
default:
goto error_exit;
}
}
res = talloc_strdup_append(res, template);
res = talloc_asprintf_append(res, ".%s", file_ext);
char *fname = mp_get_user_path(NULL, mpctx->global, res);
talloc_free(res);
return fname;
error_exit:
talloc_free(res);
return NULL;
}
static char *gen_fname(struct mp_cmd_ctx *cmd, const char *file_ext)
{
struct MPContext *mpctx = cmd->mpctx;
screenshot_ctx *ctx = mpctx->screenshot_ctx;
int sequence = 0;
for (;;) {
int prev_sequence = sequence;
char *fname = create_fname(ctx->mpctx,
ctx->mpctx->opts->screenshot_template,
file_ext,
&sequence,
&ctx->frameno);
if (!fname) {
mp_cmd_msg(cmd, MSGL_ERR, "Invalid screenshot filename "
"template! Fix or remove the --screenshot-template "
"option.");
return NULL;
}
char *dir = ctx->mpctx->opts->screenshot_dir;
if (dir && dir[0]) {
void *t = fname;
dir = mp_get_user_path(t, ctx->mpctx->global, dir);
fname = mp_path_join(NULL, dir, fname);
mp_mkdirp(dir);
talloc_free(t);
}
char *full_dir = bstrto0(fname, mp_dirname(fname));
if (!mp_path_exists(full_dir)) {
mp_mkdirp(full_dir);
}
if (!mp_path_exists(fname))
return fname;
if (sequence == prev_sequence) {
mp_cmd_msg(cmd, MSGL_ERR, "Can't save screenshot, file '%s' "
"already exists!", fname);
talloc_free(fname);
return NULL;
}
talloc_free(fname);
}
}
static void add_osd(struct MPContext *mpctx, struct mp_image *image, int mode)
{
bool window = mode == MODE_FULL_WINDOW;
struct mp_osd_res res = window ? osd_get_vo_res(mpctx->video_out->osd) :
osd_res_from_image_params(&image->params);
if (mode == MODE_SUBTITLES || window) {
osd_draw_on_image(mpctx->osd, res, mpctx->video_pts,
OSD_DRAW_SUB_ONLY, image);
}
if (window) {
osd_draw_on_image(mpctx->osd, res, mpctx->video_pts,
OSD_DRAW_OSD_ONLY, image);
}
}
static struct mp_image *screenshot_get(struct MPContext *mpctx, int mode,
bool high_depth)
{
struct mp_image *image = NULL;
const struct image_writer_opts *imgopts = mpctx->opts->screenshot_image_opts;
if (mode == MODE_SUBTITLES && osd_get_render_subs_in_filter(mpctx->osd))
mode = 0;
if (!mpctx->video_out || !mpctx->video_out->config_ok)
return NULL;
vo_wait_frame(mpctx->video_out); // important for each-frame mode
bool use_sw = mpctx->opts->screenshot_sw;
bool window = mode == MODE_FULL_WINDOW;
struct voctrl_screenshot ctrl = {
.scaled = window,
.subs = mode != 0,
.osd = window,
.high_bit_depth = high_depth && imgopts->high_bit_depth,
.native_csp = image_writer_flexible_csp(imgopts),
};
if (!use_sw)
vo_control(mpctx->video_out, VOCTRL_SCREENSHOT, &ctrl);
image = ctrl.res;
if (!use_sw && !image && window)
vo_control(mpctx->video_out, VOCTRL_SCREENSHOT_WIN, &image);
if (!image) {
use_sw = true;
MP_VERBOSE(mpctx->screenshot_ctx, "Falling back to software screenshot.\n");
image = vo_get_current_frame(mpctx->video_out);
}
// vo_get_current_frame() can return a hardware frame, which we have to download first.
if (image && image->fmt.flags & MP_IMGFLAG_HWACCEL) {
struct mp_image *nimage = mp_image_hw_download(image, NULL);
talloc_free(image);
if (!nimage)
return NULL;
image = nimage;
}
if (use_sw && image && window) {
if (mp_image_crop_valid(&image->params) &&
(mp_rect_w(image->params.crop) != image->w ||
mp_rect_h(image->params.crop) != image->h))
{
struct mp_image *nimage = mp_image_new_ref(image);
if (!nimage) {
MP_ERR(mpctx->screenshot_ctx, "mp_image_new_ref failed!\n");
return NULL;
}
mp_image_crop_rc(nimage, image->params.crop);
talloc_free(image);
image = nimage;
}
struct mp_osd_res res = osd_get_vo_res(mpctx->video_out->osd);
struct mp_osd_res image_res = osd_res_from_image_params(&image->params);
if (!osd_res_equals(res, image_res)) {
struct mp_image *nimage = mp_image_alloc(image->imgfmt, res.w, res.h);
if (!nimage) {
talloc_free(image);
return NULL;
}
struct mp_sws_context *sws = mp_sws_alloc(NULL);
mp_sws_scale(sws, nimage, image);
talloc_free(image);
talloc_free(sws);
image = nimage;
}
}
if (!image)
return NULL;
if (use_sw && mode != 0)
add_osd(mpctx, image, mode);
mp_image_params_guess_csp(&image->params);
return image;
}
struct mp_image *convert_image(struct mp_image *image, int destfmt,
struct mpv_global *global, struct mp_log *log)
{
int d_w, d_h;
mp_image_params_get_dsize(&image->params, &d_w, &d_h);
struct mp_image_params p = {
.imgfmt = destfmt,
.w = d_w,
.h = d_h,
.p_w = 1,
.p_h = 1,
};
mp_image_params_guess_csp(&p);
if (mp_image_params_equal(&p, &image->params))
return mp_image_new_ref(image);
struct mp_image *dst = mp_image_alloc(p.imgfmt, p.w, p.h);
if (!dst) {
mp_err(log, "Out of memory.\n");
return NULL;
}
mp_image_copy_attributes(dst, image);
dst->params = p;
struct mp_sws_context *sws = mp_sws_alloc(NULL);
sws->log = log;
if (global)
mp_sws_enable_cmdline_opts(sws, global);
bool ok = mp_sws_scale(sws, dst, image) >= 0;
talloc_free(sws);
if (!ok) {
mp_err(log, "Error when converting image.\n");
talloc_free(dst);
return NULL;
}
return dst;
}
// mode is the same as in screenshot_get()
static struct mp_image *screenshot_get_rgb(struct MPContext *mpctx, int mode)
{
struct mp_image *mpi = screenshot_get(mpctx, mode, false);
if (!mpi)
return NULL;
struct mp_image *res = convert_image(mpi, IMGFMT_BGR0, mpctx->global,
mpctx->log);
talloc_free(mpi);
return res;
}
void cmd_screenshot_to_file(void *p)
{
struct mp_cmd_ctx *cmd = p;
struct MPContext *mpctx = cmd->mpctx;
const char *filename = cmd->args[0].v.s;
int mode = cmd->args[1].v.i;
struct image_writer_opts opts = *mpctx->opts->screenshot_image_opts;
char *ext = mp_splitext(filename, NULL);
int format = image_writer_format_from_ext(ext);
if (format)
opts.format = format;
bool high_depth = image_writer_high_depth(&opts);
struct mp_image *image = screenshot_get(mpctx, mode, high_depth);
if (!image) {
mp_cmd_msg(cmd, MSGL_ERR, "Taking screenshot failed.");
cmd->success = false;
return;
}
cmd->success = write_screenshot(cmd, image, filename, &opts, true);
talloc_free(image);
}
void cmd_screenshot(void *p)
{
struct mp_cmd_ctx *cmd = p;
struct MPContext *mpctx = cmd->mpctx;
struct mpv_node *res = &cmd->result;
int mode = cmd->args[0].v.i & 3;
bool each_frame_toggle = (cmd->args[0].v.i | cmd->args[1].v.i) & 8;
bool each_frame_mode = cmd->args[0].v.i & 16;
screenshot_ctx *ctx = mpctx->screenshot_ctx;
if (mode == MODE_SUBTITLES && osd_get_render_subs_in_filter(mpctx->osd))
mode = 0;
if (!each_frame_mode) {
if (each_frame_toggle) {
if (ctx->each_frame) {
TA_FREEP(&ctx->each_frame);
return;
}
ctx->each_frame = talloc_steal(ctx, mp_cmd_clone(cmd->cmd));
ctx->each_frame->args[0].v.i |= 16;
} else {
TA_FREEP(&ctx->each_frame);
}
}
cmd->success = false;
struct image_writer_opts *opts = mpctx->opts->screenshot_image_opts;
bool high_depth = image_writer_high_depth(opts);
struct mp_image *image = screenshot_get(mpctx, mode, high_depth);
if (image) {
char *filename = gen_fname(cmd, image_writer_file_ext(opts));
if (filename) {
cmd->success = write_screenshot(cmd, image, filename, NULL, false);
if (cmd->success) {
node_init(res, MPV_FORMAT_NODE_MAP, NULL);
node_map_add_string(res, "filename", filename);
}
}
talloc_free(filename);
} else {
mp_cmd_msg(cmd, MSGL_ERR, "Taking screenshot failed.");
}
talloc_free(image);
}
void cmd_screenshot_raw(void *p)
{
struct mp_cmd_ctx *cmd = p;
struct MPContext *mpctx = cmd->mpctx;
struct mpv_node *res = &cmd->result;
struct mp_image *img = screenshot_get_rgb(mpctx, cmd->args[0].v.i);
if (!img) {
cmd->success = false;
return;
}
node_init(res, MPV_FORMAT_NODE_MAP, NULL);
node_map_add_int64(res, "w", img->w);
node_map_add_int64(res, "h", img->h);
node_map_add_int64(res, "stride", img->stride[0]);
node_map_add_string(res, "format", "bgr0");
struct mpv_byte_array *ba =
node_map_add(res, "data", MPV_FORMAT_BYTE_ARRAY)->u.ba;
*ba = (struct mpv_byte_array){
.data = img->planes[0],
.size = img->stride[0] * img->h,
};
talloc_steal(ba, img);
}
static void screenshot_fin(struct mp_cmd_ctx *cmd)
{
void **a = cmd->on_completion_priv;
struct MPContext *mpctx = a[0];
struct mp_waiter *waiter = a[1];
mp_waiter_wakeup(waiter, 0);
mp_wakeup_core(mpctx);
}
void handle_each_frame_screenshot(struct MPContext *mpctx)
{
screenshot_ctx *ctx = mpctx->screenshot_ctx;
if (!ctx->each_frame)
return;
if (ctx->last_frame_count == mpctx->shown_vframes)
return;
ctx->last_frame_count = mpctx->shown_vframes;
struct mp_waiter wait = MP_WAITER_INITIALIZER;
void *a[] = {mpctx, &wait};
run_command(mpctx, mp_cmd_clone(ctx->each_frame), NULL, screenshot_fin, a);
// Block (in a reentrant way) until the screenshot was written. Otherwise,
// we could pile up screenshot requests forever.
while (!mp_waiter_poll(&wait))
mp_idle(mpctx);
mp_waiter_wait(&wait);
}
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