os.makedirsの細かすぎるセキュリティの話

みんなのPython勉強会#66懇親会LT

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1. os.makedirsͷ ࡉ͔͗͢ΔηΩϡϦςΟͷ࿩ Ryuji Tsutsui ΈΜͳͷPythonษڧձ#66 ࠙਌ձLT
2. ࣗݾ঺հ • Ryuji Tsutsui@ryu22e • ࿡ຊ໦ͷϑΟϯςοΫܥاۀͰDjangoΛ࢖ͬͯWebαʔϏεΛ࡞͍ͬͯ·͢ • ৭ʑͳOSSίϛϡχςΟʹؔΘ͍ͬͯ·͢ • Python Boot CampίΞελοϑ • Shonan.pyελοϑ • Python Charity Talks in Japanελοϑ • झຯ: өըؑ৆ɾ֨ಆٕ؍ઓ ݄೔ʢ౔ʣ։࠵
   ࢀՃͯ͠Ͷʂ
3. ࠓ೔࿩͢͜ͱ • Python 3.7Ҏ্ͷos.makedirs
 ʢෳ਺֊૚ͷσΟϨΫτϦΛ࡞੒͢Δؔ਺ʣʹՃΘͬͨʮ͋Δมߋʯ ʹ͍ͭͯͷ࿩ • ͲΜͳมߋͳͷ͔ • ͳͥมߋ͞Εͨͷ͔ • ͜ͷมߋʹΑΓى͜Γ͏Δ੬ऑੑ
4. ͲΜͳมߋͳͷ͔
5. ެࣜυΩϡϝϯτΛಡΜͰΈΑ͏ • https://docs.python.org/3.7/library/os.html#os.makedirs ΑΓҾ༻ Changed in version 3.7: The mode argument no longer affects the file permission bits of newly-created intermediate-level directories. όʔδϣϯ3.7ͷมߋ: modeҾ਺͸ɺ৽͘͠࡞੒͞ΕͨதؒϨϕϧͷσΟϨΫ τϦͷϑΝΠϧύʔϛογϣϯϏοτʹӨڹΛ༩͑ͳ͘ͳΓ·ͨ͠ɻ ↓࿨༁
6. ࣮ࡍʹίʔυΛॻ͍ͯݕূͯ͠ΈΑ͏ """example.py"""
 import os from pathlib import Path # dir1΋dir2΋ύʔϛογϣϯ700Λࢦఆͨͭ͠΋Γ mode = 0o700 os.makedirs(Path.cwd() / "dir1" / "dir2", mode=mode)
7. Python 3.6Ͱͷ࣮ߦ݁Ռ $ python3.6 example.py $ stat --format='%a' dir1 dir1/dir2/ 700 700
8. Python 3.7Ҏ্Ͱͷ࣮ߦ݁Ռ $ umask 077 && python3.7 example.py $ stat --format='%a' dir1 dir1/dir2/ 700 700 $ umask 022 && python3.7 example.py $ stat --format='%a' dir1 dir1/dir2/ 755 700 $ umask 000 && python3.7 example.py $ stat --format='%a' dir1 dir1/dir2/ 777 700 $ umask 000 && python3.6 example.py $ stat --format='%a' dir1 dir1/dir2/ 700 700 EJSʢதؒϨϕϧͷσΟϨΫτϦʣͷ ύʔϛογϣϯ͸NPEFҾ਺ͷӨڹΛड͚ͣɺ VNBTLͷ஋ʹΑͬͯ݁Ռ͕มΘΔ
 ʢPdVNBTLʣ 1ZUIPO
   ͩͱVNBTLͷӨڹ͸ड͚ͳ͍
9. ͳͥมߋ͞Εͨͷ͔
10. CPythonͷιʔείʔυ͔Βgit blameͰḷͬͯ Έͨ • ʮos.makedirs('dir1/dir2', 0) always failsʯͱ͍͏Issue͕ڍ͕͍ͬͯ ͨ • https://bugs.python.org/issue19930
11. • 3.6Ͱʮos.makedirs('dir1/dir2', 0)ʯΛ࣮ߦ͢Δͱʮdir1ʯͷύʔϛο γϣϯ͕0ʹͳΓɺʮdir2ʯ͕࡞੒Ͱ͖ͳ͍ɻ
 ʢ਌σΟϨΫτϦͷύʔϛογϣϯʹॻ͖ࠐΈݖݶ͕ͳ͍ͷͰʣ • mkdirίϚϯυͰ͸ɺʮmkdir -p -m 0 dir1/dir2ʯͩͱdir1͸ ʮ0o777&~umaskʯͷύʔϛογϣϯ͕༩͑ΒΕΔɻ͜Εͱಉ͡࢓༷ ʹͨ͠΄͏͕͍͍ͷͰ͸ʁ • ٞ࿦ͷ݁Ռɺ͜ͷఏҊ͕ड͚ೖΕΒΕΔ͜ͱʹͳͬͨ ཁ໿͢Δͱ͜͏
12. ͜ͷมߋʹΑΓى͜Γ͏Δ੬ऑੑ
13. ͜ͷมߋ͕ݪҼͷDjango੬ऑੑ͕࣮ࡍʹ͋ͬͨ • CVE-2020-24583ɾCVE-2020-24584 
 ʢ2020೥9݄1೔ʹमਖ਼൛ϦϦʔεʣ • ੩తϑΝΠϧΛஔ͘σΟϨΫτϦɾΩϟογϡͷॻ͖ࠐΈઌσΟϨ ΫτϦΛ࡞੒͢Δࡍʹos.makedirsΛmode෇͖Ͱ࢖͍ͬͯΔ • umaskͷ஋ʹΑͬͯ͸ɺ͜ΕΒͷσΟϨΫτϦʹ༨෼ͳύʔϛο γϣϯΛ༩͑ͯ͠·͏Մೳੑ͕͋ͬͨ
14. ͜ͷΑ͏ʹରԠ͞Εͨ import os from pathlib import Path mode = 0o700 # modeʹࢦఆͨ͠஋ͱಉ͡ύʔϛογϣϯʹͳΔΑ͏Ұ୴umaskΛมߋ old_umask = os.umask(0o777 & ~mode) try: os.makedirs(Path.cwd() / "dir1" / "dir2", mode=mode) finally: # σΟϨΫτϦ࡞੒ޙʹumaskΛݩʹ໭͢ os.umask(old_umask)
15. ·ͱΊ • Python 3.7͔Βos.makedirsͷmodeҾ਺͸ʮதؒϨϕϧͷσΟϨΫτ ϦʯʹӨڹΛ༩͑ͣɺumaskͷ஋ʹΑͬͯύʔϛογϣϯ͕ܾ·Δ • mkdirίϚϯυͷ࢓༷ʹ߹Θͤͯ͜͏ͳͬͨ • 3.6·Ͱͱಉ͡ڍಈΛظ଴͢ΔίʔυΛॻ͘ͱɺσΟϨΫτϦʹ༨෼ ͳύʔϛογϣϯΛ༩͑ͯ͠·͏Մೳੑ͕͋ΔͷͰ஫ҙ • ճආ͢Δʹ͸os.makedirsͷલޙͰos.umaskΛݺͿ͜ͱ