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AP_Filesystem: ROMFS: fix open race conditions #29201

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merged 1 commit into from
Feb 1, 2025
Merged

AP_Filesystem: ROMFS: fix open race conditions #29201

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11 changes: 7 additions & 4 deletions libraries/AP_Filesystem/AP_Filesystem_ROMFS.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -32,6 +32,8 @@ int AP_Filesystem_ROMFS::open(const char *fname, int flags, bool allow_absolute_
errno = EROFS;
return -1;
}

WITH_SEMAPHORE(record_sem); // search for free file record
uint8_t idx;
for (idx=0; idx<max_open_file; idx++) {
if (file[idx].data == nullptr) {
Expand All @@ -42,10 +44,6 @@ int AP_Filesystem_ROMFS::open(const char *fname, int flags, bool allow_absolute_
errno = ENFILE;
return -1;
}
if (file[idx].data != nullptr) {
errno = EBUSY;
return -1;
}
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file[idx].data = AP_ROMFS::find_decompress(fname, file[idx].size);
if (file[idx].data == nullptr) {
errno = ENOENT;
Expand All @@ -61,6 +59,8 @@ int AP_Filesystem_ROMFS::close(int fd)
errno = EBADF;
return -1;
}

WITH_SEMAPHORE(record_sem); // release file record
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AP_ROMFS::free(file[fd].data);
file[fd].data = nullptr;
return 0;
Expand Down Expand Up @@ -142,6 +142,7 @@ int AP_Filesystem_ROMFS::mkdir(const char *pathname)

void *AP_Filesystem_ROMFS::opendir(const char *pathname)
{
WITH_SEMAPHORE(record_sem); // search for free directory record
uint8_t idx;
for (idx=0; idx<max_open_dir; idx++) {
if (dir[idx].path == nullptr) {
Expand Down Expand Up @@ -216,6 +217,8 @@ int AP_Filesystem_ROMFS::closedir(void *dirp)
errno = EBADF;
return -1;
}

WITH_SEMAPHORE(record_sem); // release directory record
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free(dir[idx].path);
dir[idx].path = nullptr;
return 0;
Expand Down
5 changes: 5 additions & 0 deletions libraries/AP_Filesystem/AP_Filesystem_ROMFS.h
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Original file line number Diff line number Diff line change
Expand Up @@ -19,6 +19,8 @@

#if AP_FILESYSTEM_ROMFS_ENABLED

#include <AP_HAL/Semaphores.h>

#include "AP_Filesystem_backend.h"

class AP_Filesystem_ROMFS : public AP_Filesystem_Backend
Expand Down Expand Up @@ -56,6 +58,9 @@ class AP_Filesystem_ROMFS : public AP_Filesystem_Backend
void unload_file(FileData *fd) override;

private:
// protect searching for free file/dir records when opening/closing
HAL_Semaphore record_sem;

// only allow up to 4 files at a time
static constexpr uint8_t max_open_file = 4;
static constexpr uint8_t max_open_dir = 4;
Expand Down
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